A huge chunk of a Himalayan glacier fell into the Alaknanda river system in Uttarakhand last Sunday, triggering a massive flood that washed away parts of two hydropower plants, roads and bridges in the region.

Five bodies were recovered from a tunnel in the Tapovan power project, state police chief Ashok Kumar said from state capital Dehradun.

These were the first bodies to be recovered from the site, where sludge-clearing and drilling has continued round the clock over the past seven days. A total of 35 men were at work in the tunnel when the disaster struck.

Seven more bodies were recovered from the Raini area, where another smaller power project was destroyed in the disaster.

"Chances of finding survivors in the Tapovan tunnel are quite remote. It appears that the casualties occurred soon after the disaster as the bodies were found buried in debris," Kumar said.

"It's a herculean task. We have cleared 150 metres of muck and debris from the 2.5 kilometre tunnel, but we will keep on with the rescue efforts," he added.

A total of 154 people remain missing in the flood-hit Himalayan district, Kumar said.

Villagers grazing cattle or living in low-lying areas had also been washed away.

Uttarakhand is prone to flash floods and landslides.

Scientists had begun investigations into what caused the glacier to burst as environmentalists blamed the disaster on rampant construction activities and climate change weakening the glacier.

Australian Associated Press