New Delhi - At least 12 workers were washed away when a dam that was under construction collapsed in India's north-eastern state of Sikkim, a news report said Friday.

The Rang Po dam collapsed Thursday night in eastern Sikkim and efforts were being made to retrieve the bodies from a tunnel downstream, police officials told the PTI news agency.

The small dam was being built by a private company for storing water for hydropower generation at a project nearby.

According to the officials, the dam suddenly burst because of a surge in the water level of the Rongli River caused by heavy rainfall over the past few days.

Police were investigating amid allegations that substandard materials might have been used in the dam's construction.(dpa)