The death toll from a coal mine explosion in northern China rose to 87 on Sunday as rescue crews worked in frigid temperatures to reach 21 miners still trapped underground.

A total of 528 people were working in the Xinxing mine at the time of the 2:30 a.m. Saturday explosion, the State Administration of Work Safety said in a statement. It said 418 miners escaped.

China Central Television, CCTV, displayed a diagram showing the miners were trapped about a half a kilometre underground.

Television footage showed that one entrance to the mine was blocked. Rescuers in orange suits and with breathing equipment were attempting to enter the mine through another entrance.

The massive blast cut power in the mine, as well as ventilation and communication links, hampering the efforts of the more than 300 rescue workers.

A man who answered the phone at the mine office later said ventilation and power had been restored in the mine. He said the mine's director, deputy director and chief engineer were fired on Saturday.

China's mines are the world's deadliest, but large state-owned coal mines are generally considered safer than smaller, private ones.

The government has been cracking down on unregulated mining operations, which account for almost 80 per cent of the country's 16,000 mines.

The closure of about 1,000 dangerous small mines last year helped to cut in half the average number of miners killed, to about six a day, in the first six months of this year, the government has said.

With files from The Associated Press