Hao Wenji, an official with the environmental protection department in Fenxi County of the resource-rich city of Linfen, and a local villager named Zhou Fuming, were suspected of having sent the 20 workers down an illegal pit, a source with the county's public security bureau said.

    The workers sneaked into the Weijialing pit in Fenxi County at around 7 p.m. on Sunday, but a blast went off at 9 p.m., killing them all.

    The provincial work safety administration said illegal operations started in Weijialing in 2004, but authorities soon shut down the place for safety considerations.

    The illegal operators were taking the opportunity to sneak back into the place on Sunday, when the area had been cut off by heavy snow.

    Police are relying on three miners to provide clues leading to the suspects' hideout. The three were hired for the illegal mining operation but were not sent down the pit on Sunday.

    Investigators are yet to find out whether the blast was caused by gas or explosive, though they did find detonators in the pit.

    The coal-rich Shanxi Province is notorious for mine disasters. About seven weeks ago, a gas blast killed 105 people in Linfen, the deadliest in China in the recent two years.

    Mine safety is also a major topic at the ongoing annual parliamentary session in Shanxi, with delegates proposing tougher punishment for officials who harbor, or collaborate with, illegal mine operators.