NEW DELHI (AFP) - Hope has all but faded for 13 miners trapped deep underground four days ago when an illegal "rat hole" coal pit flooded in remote northeastern India.

Emergency crews have been pumping water from the site since the accident last Thursday (Dec 13) in mineral-rich Meghalaya state, but no contact has been made with the workers believed trapped below, police say.

Authorities have declined to comment on their fate, but concede the operation was fraught with difficulty.

"We can't say anything now as rescue operations are still on," Mr Sylvester Nongtnger, local police superintendent in the area, told AFP.

"The coal pit is very deep, some 350 feet (106 metres). We are trying our best."

An Indian court had banned coal mining in the area in 2014 after environmental activists complained it was responsible for severe water pollution.

But the practice continues with locals illegally extracting coal using dangerous so-called rat hole mines.

This involves digging pits on the side of hills and then burrowing small horizontal tunnels into the hill to reach a coal seam.

At least 15 miners were killed after they were trapped inside a flooded rat hole mine elsewhere in Meghalaya in 2012. Their bodies were never recovered.