"Up till now, 10 bodies have been recovered after two more were pulled out. Coal mine authorities believe that there may be 2-3 more dead bodies inside," Jharkhand police spokesman, RK Mallick, told AFP.
"Total dead should not be more than 13 or 14, as per assessment."
He added that it was difficult to know how many may be trapped, but said close to a dozen were still unaccounted for.
Some of the workers had escaped the disaster site following the collapse, Mr Mallick said.
Images showed the dead covered with white sheets on makeshift quilts as colleagues and locals looked on at the rescue efforts.
Police and emergency workers used sniffer dogs, earth movers and their bare hands to remove giant rocks and mangled, overturned trucks to locate the trapped workers under tons of earth.
Prime Minister Narendra Modi expressed his grief on Twitter, promising to help the state government in its rescue operations.
"Saddened by the loss of lives at a mine in Jharkhand. My prayers are with those trapped inside," he said.
The mine is operated by the government-owned Eastern Coalfields Limited. Its top official, Niladri Roy, told AFP that more than 250 metres (820 feet) of the mine collapsed as workers headed towards the exit around 7:30 pm Thursday.
There was no immediate explanation for the collapse, but the government has launched an investigation into the "unprecedented" incident.
In a separate incident on Thursday, four miners were injured at a government-run coal mine in Jharkhand's Dhanbad district.
A mine official said the workers were hit after the roof of the Putki Balihari coal mine partially collapsed. Two of the workers were critically injured.
Jharkhand is one of the richest mineral zones in India, accounting for around 29 percent of the country's coal deposits. However it is also one of India's poorest areas and the epicentre of a Maoist insurgency.
In 2015, India recorded 38 deaths across 570 mining sites. The last major mining accident in India occurred in 1975, when 372 workers were killed following the flooding of Chasnala mine in Dhanbad.