A multi-agency operation to rescue an estimated 34 people trapped inside a big tunnel at Tapovan was carried out overnight after a glacier burst-triggered deluge killed 10 people in Uttarakhand's Chamoli district while over 140 are missing, officials said on Monday.

Personnel from the Indo-Tibetan Border Police (ITBP), the National Disaster Response Force (NDRF) and some state disaster response teams are clearing the tunnel that has been blocked with slush, debris and silt, and are inching closer towards the stuck workers.

"Our teams are working overnight to rescue about 30 workers who are trapped in the tunnel. Specialised equipment for such operations has been deployed. We are hopeful we will able to rescue everyone," ITBP spokesperson Vivek Kumar Pandey said in Delhi.

Around 300 ITBP personnel are currently deployed at the site, he said.

Another officer said it is estimated that around 34 people are trapped in the 'head race tunnel' or HRT.

The force's Additional Director General (Western Command) M S Rawat also reached the spot Monday morning to take stock of the situation and interacted with officers working at the site, Pandey added.

ITBP teams were seen clearing the over 1,500-metre-long tunnel, which is executed till over 1,329 metres, using earthmovers driven by local workers.

A team of senior officials, in a video provided by the force, were seen analysing the tunnel's map to find the best way of approach.

The tunnel has only one entry, an official said.

ITBP rescuers were seen carrying wooden planks which will be used to create a platform to pull out the trapped people using ropes.

Teams of the NDRF also reached the spot late Sunday night and were seen using shovels to clear the tunnel's approach.

The force has also brought along canine teams that will help them detect lives trapped underneath better.

More teams have been sent to the site on Mi-17 helicopters that landed at the helipad in Joshimath, NDRF chief S N Pradhan said in a Twitter post.

He said the agencies are working in close coordination.

Some teams from the Army have also reached the Tapovan spot, a senior official supervising the operation said.

At least 12 workers were rescued from a smaller tunnel in this area by ITBP on Sunday evening.