By Agence France-Presse
Dozens of emergency workers were pumping water out of a large trench that was flooded early Thursday near a river in mineral-rich Meghalaya state.
"We are doing our best to reach out to them. Our information is 13 people were inside at the time of flooding," police official Lethindra Sangma told AFP.
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.