Amaravati: The water levels in the Teesta river suddenly rose after a sudden cloudburst caused flooding in Lonak Lake in North Sikkim on Wednesday. It has been raining continuously for four days. Due to the cloud burst, there was a sudden flood within a few minutes, creating a huge flood. The water level suddenly rose by 15 to 20 feet, many roads and bridges were destroyed due to flash floods. Army vehicles parked at Bardung near Singtam were swept away by the flood. 23 army personnel are missing.. Search operations are going on for their whereabouts.. It is reported that many army bases along the Lachen valley were also heavily damaged due to flash floods. Several parts of National Highway 10 connecting West Bengal- Sikkim were washed away.. Many roads were closed due to flash floods. Sikkim government has declared high alert in the state..