- The October 2023 flood started at South Lhonak Lake, destroyed the Teesta Stage III dam at Chungthang and damaged long stretches of NH10.
- Since then the roads to Lachen, Gurudongmar and sometimes Lachung have closed and reopened several times, often at short notice.
- NH10 between Sevoke and Rangpo remains prone to closures in the monsoon, and the road via Lava, Algarah and Rhenock is the usual alternative.
- Build one or two spare days into any North Sikkim plan and confirm road and permit status with your operator the evening before you leave.
What happened in October 2023
On the night of 3 to 4 October 2023, South Lhonak Lake, a glacial lake high in north-western Sikkim, burst through its moraine. A wall of water, mud and boulders rushed down the Lhonak and into the Teesta. At Chungthang, where the Lachen and Lachung rivers meet, it overtopped and destroyed the dam of the Teesta Stage III hydroelectric project, and the combined surge swept on down the valley through Dikchu, Singtam and Rangpo and into the Kalimpong and Darjeeling hills.
The flood killed dozens of people, among them soldiers at an army camp near Singtam, and many more were reported missing. Bridges were washed away, houses in Chungthang and low-lying parts of Singtam and Rangpo were buried in silt, and NH10, the main road from Siliguri to Gangtok, was cut in several places along the river. Thousands of tourists were stranded in Lachen and Lachung for days and were brought out by road and by helicopter as routes were patched.
We write this not to frighten anyone away. The hills are open, people here depend on visitors, and most trips go ahead. But the flood changed the ground under the roads, and travellers who understand that plan better and worry less.
North Sikkim since the flood
North Sikkim is reached from Gangtok by the road through Phodong and Mangan to Chungthang, where it splits: one arm climbs to Lachung and the Yumthang valley, the other to Lachen, Thangu and Gurudongmar Lake. Chungthang took the worst of the flood, and both arms depend on the roads and bridges around it.
Since October 2023 the region has opened and closed in phases. In our experience, the Lachung side has generally been reachable for longer stretches than the Lachen side, and there have been long periods when tours to Lachen and Gurudongmar were simply not permitted. Heavy rain has added fresh landslides. In June 2025 a landslide hit an army camp at Chaten near Lachen, and visitors were stranded in Lachung for several days when the roads were cut again.
The practical result is that a North Sikkim permit, which is issued through registered tour operators in Gangtok, may be refused or cancelled at short notice because the district administration has closed a road. Operators know this and will usually offer a refund or a switch, for example from Gurudongmar to Yumthang. We would always ask exactly what happens if the trip is cancelled before paying.
Route status at a glance
The table below is a general picture as we understand it, not a live bulletin. Roads here can change from open to closed overnight. Read it as a guide to which routes are fragile, and check current status before you travel.
| Route | What the flood did | What to expect now |
|---|---|---|
| NH10, Sevoke to Rangpo | Long stretches undercut or washed out | Open most of the year; frequent monsoon closures |
| Lava, Algarah and Rhenock road | Not on the river, less affected | Main alternative when NH10 shuts; slower, steeper |
| Gangtok to Mangan | Landslides, not the main flood path | Usually open; monsoon slips |
| Mangan to Chungthang | Town and bridges badly damaged | Rebuilt sections; closures after heavy rain |
| Chungthang to Lachung and Yumthang | Road and bridges damaged | Open in phases; check before booking |
| Chungthang to Lachen and Gurudongmar | Severe damage, repeated slides | Long closures; most fragile route |
A local planner replies within one working day.
The Teesta valley below Kalimpong
Further south the flood hit the stretch of NH10 that runs beside the Teesta between Sevoke, Teesta Bazaar, Melli and Rangpo. This is the road most people take from Siliguri to Gangtok or Kalimpong. The flood dumped huge volumes of silt and boulders, raising the riverbed, and in the monsoons of 2024 and 2025 the river and the slopes above it caused repeated closures, some lasting days.
When NH10 is shut, traffic to Gangtok goes round through the hills, usually via Gorubathan or Malbazar to Lava, Algarah and Rhenock, or through Kalimpong and Pedong. Expect an extra two to four hours and higher reserved car fares, and shared jeeps may run fewer trips. Kalimpong town itself sits high above the river and was not flooded, and the villages of Lava, Lolegaon, Rishyap and Pedong are as open as ever; they make a good base when the valley road is troubled.
Rafting at Teesta Bazaar and riverside camps have been more irregular since the flood. If a camp or rafting trip is part of your plan, ask the operator directly whether they are running that week.
How to plan a trip that survives a closure
The habits that make a hill trip safe have not changed, they have just become more important. We plan North Sikkim and Teesta valley trips with slack in them and with a fallback for every leg.
- Keep one spare day before your flight or train home, two if North Sikkim is in the plan.
- Book North Sikkim as the middle of your trip, not the end, so a delay does not cost you a flight.
- Ask your operator for the refund or switch policy if roads or permits are closed, in writing.
- Check the Mangan district and Sikkim Tourism notices, and ask your driver the evening before departure.
- Avoid driving the Teesta valley after dark in the monsoon, and do not stop under fresh landslide scars.
- Carry enough cash for three extra nights; ATMs above Mangan are few and networks fail in bad weather.
- Buy travel insurance that covers trip interruption, and keep a printed copy of your permits and ID.
Good alternatives if the north is closed
A closed road does not have to mean a lost holiday. If Lachen and Gurudongmar are shut, Lachung and Yumthang may be open; if both are shut, Dzongu, the Lepcha reserve west of Mangan, has homestays that are reached by a shorter road and offer some of the most interesting village stays in Sikkim, when its own roads are open. Kabi Lungchok and the monastery at Phodong are easy half-days from Gangtok.
For snow and a high pass from Gangtok, Tsomgo Lake and, for Indian nationals, Nathu La are on the other side of the state and were not touched by the flood, though they have their own winter closures. On the Kalimpong side, Lava and the Neora Valley forests, or the Silk Route villages of East Sikkim, make a fine week without going near the Teesta at all.
What has not changed
The people of Lachung still run their homestays, the yaks still graze the Yumthang valley in summer, and Gangtok, Kalimpong and Darjeeling are all working, welcoming towns. The flood was a disaster for many families along the river, and the best thing a traveller can do is to keep coming, spend money locally and be patient with a road crew clearing a slide.
Season still matters more than anything else. The months with the fewest closures are October and November, after the monsoon has finished and before winter snow, and March to May, when roads are dry and the rhododendrons are out around Lachung and Yumthang. June to September is when most landslides happen, and December to February brings snow that can close the roads above Lachen and Lachung for days. If you have a choice, pick autumn or spring for North Sikkim, and keep the monsoon for the towns of Kalimpong and Darjeeling, where a wet day still leaves plenty to do.
We think of it this way: in these hills, the road is part of the trip. Travel with a buffer, keep your plans loose, listen to drivers who make the run every week, and check current status before you travel.
Questions people ask
Good to know
Is North Sikkim open for tourists after the Teesta flood?
Parts of it are open in phases. Since October 2023, the Lachung and Yumthang side has generally been open for longer stretches than Lachen and Gurudongmar, which have had long closures. Status changes with weather and repairs, sometimes overnight. Ask a registered Gangtok operator and watch the Mangan district notices, and check current status before you travel.
Is NH10 open between Siliguri and Gangtok?
Most of the year, yes, but the stretch along the Teesta between Sevoke and Rangpo closes often in the monsoon because of landslides and river damage since the 2023 flood. When it is shut, vehicles use the longer hill road via Lava, Algarah and Rhenock or via Kalimpong and Pedong, adding two to four hours. Check current status before you travel.
What caused the 2023 Teesta flood?
A glacial lake outburst. On the night of 3 to 4 October 2023, South Lhonak Lake in north-western Sikkim breached its moraine and sent a surge down the Teesta. At Chungthang it destroyed the dam of the Teesta Stage III hydroelectric project, and the combined water swept through Dikchu, Singtam and Rangpo, damaging roads, bridges and towns.
Is it safe to visit Gangtok and Kalimpong now?
Yes, both towns sit well above the river and are open and working. The risk lies mainly on the roads along the Teesta, especially in the monsoon from June to September. Travel by day, keep a spare day in your plans and follow local advice on landslides. Autumn and spring are the most reliable seasons for these routes.
Will I get a refund if my North Sikkim tour is cancelled?
It depends on your operator. When the administration closes a road, permits are not issued, and most registered Gangtok operators offer a refund of unused costs or a switch to another destination such as Yumthang or Tsomgo. Policies vary, so ask for the cancellation terms in writing before paying, and carry travel insurance that covers interruption.
