"The labourers were trapped in a power house when it was flooded by water from the tunnel. Three bodies were recovered from the power house and the driver of a car which was swamped by landslide was also found dead," project manager E Lyngdoh said.
Six persons and five others working in the tunnel were untraced, he said.
SP M K Singh said a team which comprised police personnel were carrying out rescue operations.
Incessant rains for the last two days led to overflow of water in the dam and triggered landslides at the site of Rs 900 crore 84 MW power project.
Lyngdoh said there was a sudden flash of water from 4.