Beijing ? A coal mine blast in northwestern China killed 27 people, the government said Sunday, as rescuers searched for five remaining workers still missing in the mine’s underground shafts.

Thirty-nine miners were working underground when the gas blast occurred Saturday afternoon at the Wayaobao Coal Mine in Shaanxi province, China’s State Administration of Coal Mine Safety said on its Web site.

Seven people managed to escape, and 27 workers were confirmed dead, the official Xinhua News Agency said. Rescuers were still searching for five people still missing, it said.

It wasn’t immediately clear what caused the gas blast. Xinhua said investigations were under way.

Police have placed the owner and management of the Wayaobao mine under watch, sealed the mine’s records and frozen its accounts, according to Xinhua.

Thousands of workers are killed each year in China’s mines, the world’s most deadly. Fires, floods and explosions occur almost daily despite repeated safety crackdowns, mostly because of lax enforcement of safety rules and poor equipment.