The death toll from a blast at a coal mine in China has risen to 34, an official said Sunday, as rescuers continue to search for workers still trapped underground amid fading hopes of finding survivors.

The mine in the southwestern province of Yunnan was hit Thursday by a "coal and gas outburst" -- a sudden and violent ejection of coal, gas and rock from a coal face -- trapping 43 workers underground. Nine are still missing.

The news comes as a separate accident hit the northwestern province of Gansu early Sunday, when a flood at a coal mine trapped seven workers underground and triggered another rescue operation, the official Xinhua news agency said.

In Yunnan's Shizong county, meanwhile, rescuers have been taking turns heading down the pit to search for survivors and at least 240 tonnes of coal dust have been removed.

"It's very dangerous for rescuers because the gas is still very condensed," an official at the provincial work safety administration told AFP, adding 34 bodies had been found so far.

"And in closed conditions, the ventilation doesn't work well," said the official, who refused to be named.

The provincial rescue headquarters said on Saturday that the air was thin in the shaft and "the chances of survival for the trapped miners are slim."

The chief of China's work safety watchdog, Luo Lin, described the mine's safety measures as "very poor" and blamed lax supervision by local authorities.

The bosses of the mine -- which was operating without a licence after its permit was revoked a year ago, according to Xinhua -- have been detained and an investigation is under way.

Coal mine accidents are common in China, where work safety is often neglected by bosses seeking a quick profit.

Last year, 2,433 people died in coal mining accidents in the country, according to official statistics -- a rate of more than six workers per day -- but labour rights groups say the true figure may be much higher.

The accident in Yunnan comes days after a rock blast in a coal mine in the central province of Henan trapped dozens of workers underground.

Most were eventually pulled out after a 40-hour rescue operation, though 10 were killed.

Last month, a gas explosion at a state-owned coal mine in neighbouring Hunan province left 29 miners dead.

And earlier in October, blasts at mines in the southwestern city of Chongqing and the northern province of Shaanxi killed 13 and 11 miners respectively.

China's Vice Premier Zhang Dejiang was quoted as saying by Xinhua that "the latest coal mine accidents ring the alarm, warning us that accident prevention is a complex, difficult, and urgent task."