Heap of mud caved-in at the entry point of Lalmatia mines of Eastern Coalfields Limited (ECL) in Godda district, the police said.
At the time of the cave-in at the Rajmahal Open Cast Mines of Paharia Bhorya site, more than 40 vehicles were inside.
Rescue operation could not begin due to night fog, the police said.
The National Disaster Response Force (NDRF) team was likely to reach here by noon, officials said.
“The exact number of people and vehicle trapped inside is not known. This could only become clear after the rescue operation starts,” said Harilal Chauhan, Godda Superintendent of Police, earlier.
The locals said that there was crack in the heap of mud which collapsed and blocked the entry point of the mine.
Mining operations were taking place about 200 feet beneath the ground.