Four workers have been trapped in the tunnel of Kalanga Gad Hydropower in Bajhang district since 3 pm Sunday.

According to project officials, the labourers who had entered the tunnel to resume work after Dashain-Tihar holidays have fallen unconscious.

The workers—Karna Bahadur Shahi, Mahendra Bahadur Shahi, of Gurans Rural Municipality of Dailekh district, Mahendra Saud, of Turma Khand Rural Municipality, Shersingh Dhami, of Bungal Rural Municipality Bajhang—had gone inside the tunnel in Dadimgada on a tractor.

According to Dil Bahadur Rana, a tractor driver, the four people fell off the tractor when the vehicle reached halfway through the tunnel. He added that he drove the tractor out of the tunnel after he too experienced difficulty in breathing.

Project officials suspect the labourers could have fallen unconscious due to lack of oxygen.

After the incident, teams of Nepal Police, the Armed Police Force, the Nepal Army and locals have arrived on the scene for rescue operations. Though some security personnel have entered the tunnel with oxygen cylinder, they have not been able to retrieve the workers yet, said local journalist Makarraj Dhami.

According to Deputy Superintendent Ganesh Bom of District Police Office Bajhang, an Armed Police Force team comprising underwater rescuers have been called from Kathmandu.

The tunnel of the under-construction 75-megawatt hydropower project is 1600-metre long.