At least 23 Army personnel went missing on Wednesday morning due to a flash flood in the Teesta River in Sikkim's Lachen Valley.

Some Army vehicles have been submerged in the flash flood, defence sources confirmed.

A search operation has been launched.

The Army vehicles were parked at Bardang near Singtam when the flash flood occurred triggered by possibly a glacial lake outburst.

The water level rose up to 15-20 feet high downstream washing away several buildings and structures in North Sikkim's Chungthang. A portion of NH-10 in Melli connecting Sikkim with West Bengal was washed away in the flash flood.

A flash flood alert was issued in Sikkim after the cloud burst in Singtam. Chief minister Prem Singh Tamang took stock of the flood-like situation.

What is cloudburst?

A very sudden and heavy rainfall which is confined to a small area is called a cloudburst. When a small area receives more than 100 mm of rain in around one hour, it is said to be a cloud burst.

What is a flash flood?

A flash flood is the sudden flooding of a small area which can be caused by various factors including heavy rain, cloudburst, dam break etc.

What is a Glacial Lake Outburst Flood?

GLOP is an outburst flood when a dam containing a glacial lake breaches,

Sikkim has been receiving heavy rainfall in the past few days. The flash flood, however, could be attributed to the Glacial Lake Outburst Flood (GLOF)which is caused by the failure of a dam containing a glacial lake.

According to reports, the GLOF took place in Lhonak Lake. Coupled with heavy rain, a huge amount of water flowed into Teesta. As Sikkim is still under red alert with a heavy rainfall warning, the flood situation in the state is likely to worsen.