At least eight people died and 102 others, including 22 army personnel, were reported missing on Wednesday after the Teesta turned turgid by a cloudburst-induced water surge and caused havoc in four districts, sweeping away people, buildings, roads, bridges, dams, defence installations and vehicles.

The cascading effect was felt in neighbouring Bengal as the mighty river roared through the mountains and inundated large parts of Kalimpong, Jalpaiguri and Cooch Behar before gushing towards Bangladesh, where the effect is expected to be clear on Thursday.

“The death toll is eight as of now, but it is sure to rise,” a senior Bengal government official who has been coordinating with his counterparts in Sikkim had said earlier in the day. Three of the bodies were retrieved from the gate of the Teesta barrage in Jalpaiguri’s Gajoldoba.

As the Teesta swept away stretches of NH10, the principal highway that connects Sikkim and Kalimpong district of Bengal with Siliguri and the rest of the country, scores of tourists got stuck in the Himalayan state, prompting the Bengal government to plan immediate evacuation measures in consultation with the authorities in Gangtok.

The governments of Sikkim, which declared high alert, and Bengal and several state and central agencies have begun relief, rescue and restoration operations on a war footing. At least 23,000 people in Sikkim have been affected by the flash flood and 2,000 have been evacuated.

According to the Sikkim disaster management authority, the cloudburst took place above the South Lhonak Lake in Mangan district in the state’s north on Tuesday night and caused an unusual rise in the water level along the Teesta river basin in the early hours of Wednesday.

“The river caused severe damage in Mangan, Gangtok, Pakyong, and Namchi districts of Sikkim. It has washed away at least 11 bridges in the state. As a result, road connectivity has snapped in many areas,” a Sikkim government official said.

“The Toong bridge and the Phidang bridge, two bridges in Minshithang and one bridge each at Zema and Ritchu, all in Mangan district, were swept away.... In Gangtok, which is in the eastern part of the state, the Indrani bridge and the L.D. Kazi bridge over the Teesta that connects the district with Namchi, have also been swept away. The Teesta Urja dam in Chungthang has been washed away,” the source added.

In Singtam and Rangpo, the town that is on the Bengal-Sikkim border, vast stretches went underwater. As the water receded, hundreds of vehicles and houses were found buried under the slush that the river had carried with it. The sewage lines of both places were severely damaged.

As the Teesta carried excess waters downstream, it wreaked havoc on Melli, a small hamlet located in Kalimpong. A number of buildings on the riverbank were swept away and a stretch of NH10 was destroyed. The swollen river caused similar damage to the highway at two other locations — near Teesta Bazaar and in Likhubhir (both in Kalimpong district) — prompting the district administration to halt traffic along the route.

The engorged river also flooded both banks downstream in Jalpaiguri district and the Mekhliganj sub-division of Cooch Behar. From Mekhliganj, the river enters Bangladesh.

One of the 23 soldiers has been rescued and his condition was stated to be stable.

Unlike Sikkim, where casualties have been reported and people have been reported missing, the damage could be mitigated in Bengal as the administration shifted people from the riverbank to safer places before the waters came charging in, said a source.

With the Teesta damaging the highway and some localities on its banks, Bengal chief minister Mamata Banerjee spoke with senior officials over the phone from her residence and announced the opening of a control room with helpline numbers.

She promised all possible help to the Sikkim government to battle the disaster. Senior ministers and officers have been dispatched to north Bengal from Calcutta to monitor relief and rescue work, Mamata said.

“Close vigil is being kept to ensure no loss of life in this grave calamity,” she posted in X.

P.S. Tamang, the chief minister of Sikkim who visited some of the affected areas, said his government was making all efforts to speed up the rescue and relief operation.

“I want to assure that the government is fully committed to providing all necessary assistance and relief to those in need. We understand the magnitude of the situation and are mobilising all available resources to ensure the safety and well-being of our citizens,” he said in a statement.

Twenty-two relief camps have been opened in Sikkim.

Late on Wednesday evening, Sikkim chief secretary V.B. Pathak joined a virtual meeting of the national crisis management committee chaired by Union cabinet secretary Rajiv Gauba to review the damage caused by the flash flood. It was decided that three additional platoons of the NDRF would be stationed at Chungthang, Rangpo and Singtam.

The NDRF team for Chungthang will be air-lifted once the weather improves. “There are reports that 12 to 14 people are stranded in a tunnel in Chungthang. They will be evacuated (air-lifted) on priority. After that, the stranded tourists will be evacuated. As road connectivity to Chungthang, Lachen and Lachung (all in Mangan district) has snapped, essential commodities and supplies will also be airlifted and distributed among the people,” said a source.

“The restoration of NH10 will be the most important task. The Centre has given instructions to the Bengal government, Border Roads Organisation and the National Highways & Infrastructure Development Corporation Ltd,” the source added.

Prime Minister Narendra Modi called up Tamang. “Spoke to CM Shri @PSTamangGolay and took stock of the situation in the wake of the unfortunate natural calamity in parts of the state. Assured all possible support in addressing the challenge. I pray for the safety and well-being of all those affected,” Modi posted on X.

The devastation caused by the water surge in the Teesta — tamed in recent years following the construction of a slew of dams — brought back memories of a similar mayhem caused by the mighty river in Sikkim and Bengal in 1968.