Kolkata, July 22 -- Three more dead bodies were retrieved from the under-construction tunnel of the Teesta Stage-VI Hydel Project at Samardung in South Sikkim on Wednesday, where a methane explosion took place earlier this week, taking the death toll to 15, even as 10 people still remain missing, officials said.

Rescuers, who went inside the tunnel with breathing apparatus looking for trapped survivors, described the tunnel as pitch-dark, hot, full of poisonous gases and muddy.

"Conditions are very bad inside. It is pitch-dark and hot inside. The tunnel is full of poisonous gases such as methane and carbon monoxide. The floor of the tunnel is full of mud and our legs were frequently getting stuck," said a member of the rescue team of Co...