Rescuers working in frigid cold and darkness tried to reach 66 people believed trapped a third of a mile (half a kilometer) underground after a huge gas explosion Saturday ripped through a coal mine in northern China, killing at least 42 people.

The pre-dawn blast at the state-run Xinxing mine in Heilongjiang province near the border with Russia is latest to hit China's deadly mining industry. Authorities say parlous safety is improving, but hundreds still die in major accidents each year.

Television footage showed smoke billowing out of the mine after the explosion went off, caused by a gas build- up. It caused a building to collapse nearby.

Some 528 miners were underground at the time. The State Administration of Work Safety said 389 of them managed to escape.

Of the rest, 31 miners were rescued, including six now in serious condition in hospital, China Central Television reported. Some 42 bodies have been recovered and rescuers were searching for 66 others still believed trapped in the mine.

CCTV displayed a diagram showing the miners trapped about a third of a mile underground. 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.

On land, where snow dusted the ground, overnight temperatures were expected to drop as low as minus 14 Fahrenheit, according to the Central Meteorological Station.

Vice Premier Zhang Dejiang visited some of miners recovering in hospital Saturday afternoon.

The official Xinhua News Agency quoted Wang Xingang, one of those rescued, recounting how the blast inside the mine had briefly knocked him out.

"When I regained consciousness, I groped my way out in the dark and called for help," said the 27-year-old electrician.

China's mines are the world's deadliest, and the blast only underscores the difficulties the government faces in trying to boost safety in an industry which is vital to its vast population and booming economy. The country depends on coal to generate about three-quarters of its electricity.

Large state-owned coal mines, such as Xinxing, are considered safer than smaller, private ones.

Xinxing is located near the border with Russia, about 250 miles northeast of the provincial capital, Harbin. It is run by a major state-owned enterprise, according to the Web site of its owner, the Hegang city branch of the Heilongjiang Longmei Holding Mining Group. It says the Hegang branch has more than 88,000 employees.

In numerous telephone calls to the mine, officials refused to give any information about Saturday's accident.

The government has been cracking down on unregulated mining operations, which account for almost 80 percent of the country's 16,000 mines. It says the closure of about 1,000 dangerous small mines last year has helped it cut fatalities.

The average number of miners killed has halved, to about six a day, in the first six months of this year, the government has said. It blames failure to follow safety rules, including a lack of required ventilation or fire control equipment, for most of the deaths.

Major accidents persist. In the first nine months of this year, China's coal mines had 11 such incidents with 303 deaths. Gas explosions were the leading cause, the government said.

A blast at the Tunlan coal mine in northern China's Shanxi province in February killed 77 people in China's worst industrial accident in a year.