The toll in the collapse of a tunnel that was being constructed in Sikkim’s Namchi district has increased to 20, reported The Indian Express on Wednesday. Five more persons remained trapped inside.

The tunnel was part of the Teesta Stage VI Hydroelectric Project of the National Hydroelectric Power Corporation in the Samardung area. It was being constructed to transport high-pressure water from the reservoir to the powerhouse.

The tunnel collapsed on Monday after a “sudden explosion of trapped/embedded suspected methane gas within the rocks, resulting in dense smoke and toxic gases”, stated the National Hydroelectric Power Corporation.

Twenty-seven persons were trapped inside the tunnel, of whom two managed to come out, The Times of India quoted Chief Minister Prem Singh Tamang as saying.

Out of the 25 trapped inside, 20 are confirmed dead, said Namchi Superintendent of Police Sonam D Bhutia, according to The Indian Express.

Bhutia added that 12 bodies had been recovered during the search and rescue operations.

Rescuers fear that the toll may increase as operations are ongoing, Deccan Herald quoted unidentified police officials as saying.

Officials said on Monday that rescue workers had experienced dizziness and lost consciousness while trying to reach the trapped persons, hindering operations.

Tamang has announced a compensation of Rs 4 lakh each for the families of the dead and Rs 50,000 for injured persons.

“I am deeply saddened by the tragic incident,” he wrote on social media. “My heartfelt condolences go to the families of the workers who have lost their lives.”

The prime minister’s office announced a payment of Rs 2 lakh for the families of workers who were killed. The injured would be given Rs 50,000.

Edited by Nachiket Deuskar.