A sudden heavy rainfall triggered flash floods in the northeastern Indian state of Sikkim, killing five civilians and leaving 23 army soldiers missing Wednesday, the army and news reports said.

The flooding occurred along the Teesta River in the Lachen Valley, an army statement said, adding that some army camps and vehicles were submerged under mud and that search efforts were underway. The army said water released from a nearby dam also caused water levels to rise.

Five bodies of civilians were recovered from the Golitar and Singtam regions, the Press Trust of India news agency cited Magistrate Mahendra Chettri as saying.

Defense authorities said that 80 residents have been safely evacuated. The agency reported that a bridge over the Teesta River was also washed away in the floods early on Wednesday.

Several towns, including Dikchu, Singtam and Rangpo in the Teesta basin, were flooded. Schools in four districts have been shut for four days, the state education department said.

Parts of a highway that links Sikkim, the state capital, with the rest of the country were washed away, PTI said.

The flooding was caused by cloudbursts — sudden, very heavy rain. It happens when more than 10 centimeters of rainfall occurs within 10 square kilometers within an hour. Cloudbursts have the potential to cause intense flooding and landslides affecting thousands of people.

The mountainous Himalayan region, where Sikkim is located, has seen heavy monsoon rains this season. Nearly 50 people died in flash floods and landslides in August in nearby Himachal Pradesh state, while record rains in July killed more than 100 people over two weeks in northern India, as roads were waterlogged and homes collapsed.

Disasters caused by landslides and floods are common in India’s Himalayan region during the June-September monsoon season. Scientists say they are becoming more frequent as global warming contributes to the melting of glaciers there.

In February 2021, flash floods killed nearly 200 people and washed away houses in Uttarakhand. (AP)