Hegang, China ? Rescuers worked in frigid cold to reach 21 miners trapped underground today as the death toll from a huge gas explosion in a northern Chinese mine jumped to 87 — the deadliest blast to hit the beleaguered industry in nearly two years.

The pre-dawn blast Saturday at the state-run Xinxing mine in Heilongjiang (pronounced HAY-long-jeeahng) province near the border with Russia was the latest to hit China’s mining industry — the world’s deadliest. Authorities say safety was improving, but hundreds still die in major accidents each year.

The death toll more than doubled overnight, reported the official Xinhua News Agency. A duty officer at Xinxing’s work safety authority and an employee at the company that owns the mine confirmed 87 had died.

Ventilation and power were restored in the mine, said the employee, who refused to give his name because he was not authorized to speak to the media. The mine’s director, deputy director and chief engineer were fired Saturday, he said.

A total of 528 people were working in the Xinxing (pronounced shin-shing) mine at the time of the 2:30 a.m. explosion Saturday, the State Administration of Work Safety said in a statement. Xinhua reported 420 escaped.

Television footage showed smoke billowing out of the mine after the blast that resulted from a gas build-up. The explosion caused a nearby building to collapse.

State-run CCTV displayed a diagram showing the miners trapped about a third of a mile (half a kilometer) underground. Footage showed one entrance was blocked, and rescuers in orange suits with breathing equipment attempted to enter through another.

Overnight temperatures dropped as low as minus 10 degrees Celsius, according to the Central Meteorological Station.

Wang Xingang, one of those rescued, recounted how the blast briefly knocked him out.

“When I regained consciousness, I groped my way out in the dark and called for help,” Xinhua quoted the 27-year-old electrician as saying.

In December 2007, a gas explosion in northern China’s Shanxi province coal mine killed 105 people.