Beijing  - The death toll from a gas explosion at a coal mine in north-eastern China rose overnight to 87, with 21 workers still trapped, local media reported Sunday.

The explosion occurred early Saturday in the Xinxing mine in Hegang City, Heilongjiang province, with 528 miners underground.

By Sunday morning, 87 bodies had been retrieved, 420 workers had escaped and 21 others were still missing, the official Xinhua news agency reported.

More than 100 rescue teams were working at the site, and operations were being overseen by China's vice premier, Zhang Dejiang, the China News Service reported.

At the time of the explosion, an evacuation was underway due to a warning about gas levels in the shaft, according to state broadcaster, CCTV.

"I passed out for a while. I found I was shrouded by heavy smoke, when I regained consciousness. I groped my way out in the dark, and called for help," 27-year-old worker Wang Xingang told Xinhua from his bed in the Hegang Mining Bureau Hospital.

The blast came as the government is trying to reform China's notoriously dangerous mining industry, by closing illegal operations and reducing the number of small and medium-sized mines through mergers.

While the illegal, and small and medium-sized mines, have high production output, they also have poor safety and environmental records.

Saturday's accident was also a reminder of ongoing safety concerns at even large state-owned mines.

An investigation into the cause of the gas explosion was being led by the chief of China's State Administration of Work Safety, Luo Lin, local media reported.

China's official mining death toll was 3,215 last year, but industry analysts suspect the actual figure to be higher. (dpa)