Dozens of miners have been trapped underground and are feared dead after a blast at a coal mine in the eastern Ukrainian rebel stronghold of Donetsk, with rescuers saying the chance of finding many survivors was slim.

Mine officials said the explosion was not linked to fighting at the nearby frontline in the war between Moscow-backed rebels and Ukraine government forces. Kiev accused the separatists of holding up the rescue effort by restricting access.

Outside the gates of the Zasyadko mine, about 30 relatives clamoured for information about any survivors.

Injured miner Sergei Baldayev said five bodies had so far been retrieved from the area of the blast in a shaft deep underground.

The sister of one miner who was in the pit at the time of the explosion, Alexei Novoselsky, stood in tears.

Donetsk has been the scene of heavy fighting between Moscow-backed separatist rebels, who control the region, and forces loyal to the government in Kiev.

A ceasefire has sharply reduced the violence in the past week. The neighbourhood around the mine has come under artillery fire, with fragments from Grad rockets visible on surrounding roads, but mine officials said the explosion was unrelated to the fighting and most likely caused by gas.

In Kiev, Ukrainian Prime Minister Arseny Yatseniuk said rescue workers had been dispatched by the central authorities, "but the Russian terrorists did not let them reach the scene of the accident," he said, using a term commonly used by Kiev to describe the separatists.

Figures given by medical workers at the scene, miners and a mine official speaking on condition of anonymity pointed to there being about 50 miners still underground.

Asked what were the chances of trapped miners surviving, a medical worker said: "It's getting smaller and smaller all the time, because of the methane, the hot air, burns to the airways."

She said two buses had been brought to the mine in preparation for carrying away the bodies of the dead.