State-run hydropower major NHPC on Tuesday confirmed that 10 people have died after a suspected methane gas burst triggered an explosion inside an under-construction tunnel at its Teesta Stage VI Hydroelectric Project in Sikkim, saying 25 personnel were trapped in the incident and rescue operations remain underway.The incident occurred at 1.04 pm on Monday inside the Head Race Tunnel (HRT) at the Teesta Stage VI project in Samardung, South Sikkim, after a sudden burst of suspected methane gas trapped inside rock formations led to an explosion, generating dense fumes and toxic gases, the company said in its first official statement on the incident.Also Read: 10 killed in Sikkim tunnel collapse, rescue operation underway"As per the latest information from the site, 25 personnel were trapped inside the tunnel, out of which 10 casualties have been reported so far," NHPC said, adding that a detailed investigation would be undertaken to ascertain the cause of the accident.The company said it immediately activated emergency response protocols and is coordinating rescue efforts with the district administration, the National Disaster Response Force (NDRF), State Disaster Response Force (SDRF), local authorities and other emergency agencies. A specialised rescue team from the Directorate General of Mines Safety (DGMS) has also reached the site.NHPC said its top management has reached the project site and is working with rescue teams and local authorities to evacuate the trapped personnel. Site engineering teams are working round the clock to stabilise the tunnel environment and assist rescue operations.According to Namchi Police, 10 bodies had been recovered till 9.30 am on Tuesday. Seven victims have been identified, including four from West Bengal's Jalpaiguri and one each from Assam, Punjab, Uttarakhand's Dehradun and Namchi in Sikkim. Three bodies remain unidentified.Sikkim Chief Minister Prem Singh Tamang said the under-construction tunnel at the NHPC Teesta Stage VI Hydroelectric Project caved in following a landslide. He said Prime Minister Narendra Modi had spoken to him to enquire about the rescue operations and assured all possible assistance from the Centre.Earlier, district officials had said the rescue operation was complicated by the presence of toxic gas inside the tunnel, with several rescue personnel experiencing dizziness and losing consciousness while attempting to reach the trapped workers. The gas is believed to have naturally emanated from underground rock formations disturbed by the landslide.NHPC said it remains committed to extending full support to the rescue agencies and the affected families. "In this hour of grief, prayers of NHPC family are with the affected families during this difficult time," it said.