Rescue operations by multiple state and central agencies continued for the fourth day on Thursday to locate trapped miners inside an illegal rat-hole coal mine in Dima Hasao district of Assam, officials said.

The search operations resumed early in the morning after the dewatering exercise all night and the Remotely Operated Vehicle (ROV) has gone inside the flooded shaft, a senior official of Assam Police told PTI.

"So far, nothing has been detected by the ROV. It is trying very hard to locate the trapped miner despite the extremely hostile and difficult situation. The water inside is totally blackened and it is creating problems in finding anything," he added.

Additionally, four deep divers from the Navy also went inside the flooded shaft to find the trapped miners, the official said.

A united effort is being made by the Navy, Army, NDRF, SDRF, ONGC, Coal India and district administration to trace the workers trapped inside.

The labourers were on Monday trapped inside the 3-Kilo Coal Quarry in Umrangso area, around 250 km from Guwahati, after a sudden gush of water flooded the site.

According to employees of the quarry, there were around 15 workers inside the illegal mine when water breached one of the walls and flooded the entire shaft and tunnels.

"We were told by the miners that nine were missing and the rest escaped the tragedy. Out of them, one body was retrieved yesterday," the official said.

He said that Coal India has flown in a heavy pressure pump with a capacity of 500 gallons per minute from Maharashtra and it has reached Silchar airport in neighbouring Cachar district.

"One Mi-17 chopper will transport the pump parts in 2-3 sorties and then it will be assembled here at the site. Already 5-6 pumps are working, but heavy siltation in water is creating problems for the pumps. We now need heavy submersible pumps and it is being arranged," the official said.

He confirmed that it was a "complete rat-hole mine", which is totally illegal after a ban by the authorities concerned.

The National Green Tribunal (NGT) had banned rat-hole mining in 2014. However, coal is still extracted by this dangerous method in the Northeast.

"The shaft itself is 310 feet deep. Multiple channels were carved out through rat-hole technique from the shaft. We assume that a wall of one of the channels was breached and the entire shaft was flooded.

"There is also a possibility that one of the channels reached an unused nearby mine that was already flooded. Another possibility is one channel might have reached an underground reservoir and water gushed in suddenly. All these are probable theories, which we cannot confirm at this moment," an expert monitoring the rescue operations told PTI.

The body of one of the nine missing workers was recovered by Army divers on Wednesday. They located the body, identified as Ganga Bahadur Srestho from Udaypur district of Nepal, 85 feet below the surface.

Except for the headline, this story has not been edited by The Telegraph Online staff and has been published from a syndicated feed.