XIANGNING: Anxious relatives of 153 workers trapped in a flooded mine in northern China milled helplessly above ground Tuesday, demanding action and answers as rescue efforts stretched into the third day with no communication from those stuck deep underground.

Some 1,000 rescue workers were rotating on shifts to try to drain enough water to reach the trapped miners, but the rescue effort could take days.

It was unclear if anyone was still alive in the shafts, some of which extended a half-mile (one kilometer) into the earth.

The accident could be one of the worst mining disasters in recent years if rescue efforts fail and would set back marked improvements in mining safety.

"Their situation until now is still unknown so that is making everyone very worried," said Liu Dezheng, a chief engineer with the work safety bureau in northern China's Shanxi province, where the mine is located.

Liu warned any rescue was still days away and said the 1,000 rescuers were rotating on four-hour shifts to make sure they got enough rest in the days ahead.

"This is not something that can be achieved in one or two days," Liu said. "(Rescuers) must be prepared to work at least seven days and seven nights."

The sudden flood Sunday afternoon at the state-owned Wangjialing coal mine may have been triggered when workers dug into a network of old, water-filled shafts. Such derelict tunnels are posing new risks to miners across China even as the country improves safety in its notoriously hazardous mines, where accidents kill thousands each year.

Family members were becoming increasingly frustrated with what they said was the slow pace of the rescue effort and complained that they weren't seeing water being pumped out of the flooded mine.

"We need to see some action to make us feel like they are doing all they can," said Long Liming, brother-in-law of one of the trapped miners. "They have the materials, the pipes are here, why aren't they getting to rescuing people?"

Zhao Chuan, a rescue worker who helped show reporters pipes and pumping equipment, insisted there was an around-the-clock effort to clear the water from the mine, but that it was being hampered by intermittent electricity cuts.

State television said the workers were trapped in nine different places in the mine, which was flooded with up to 5 million cubic feet (140,000 cubic meters) of water.

Authorities were not only worried about the flood. Gases from the abandoned shafts may have flowed into the mine, bringing new dangers such as explosions or poisoning.

Dozens of relatives, including women carrying small children, gathered near the mine office, demanding rescuers do more to reach their family members. A few amid the crowd of about 60 people shouted at police who were trying to keep them from rushing into the office, though the scene was generally peaceful.

Tang Yinfeng, a migrant worker from south China's Hunan province, said two of her younger brothers were trapped underground. "I want to bring oxygen tanks down," said Tang, 49. "I want to save them myself."

China's State Administration of Work Safety said 261 workers were inside the mine when it flooded, and 108 escaped or were rescued.

"We can't get in touch with the people down there," said miner Li Jianhong, 33, who was helping move pipes to suck water from the shaft. "If they haven't drowned yet, they might have suffocated from a lack of oxygen."

Officials have yet to declare the cause of the accident, but experts said it was likely that workers broke into the old shafts or pits of derelict mines that had filled with water.

David Feickert, a coal mine safety adviser to the Chinese government, said hidden shafts are a common cause of mine floods. Shanxi would be particularly vulnerable, he said because "Shanxi is an area where they have very extensive mining, a lot of old mines."

Though China's mining industry is still the world's deadliest, it has dramatically improved its safety record in recent years.

Accidents killed 2,631 coal miners last year, fewer than half the 6,995 deaths in 2002, the most dangerous year on record, according to the State Administration of Coal Mine Safety. That means on average more than seven miners die every day, down from 19 in 2002.

Much of the safety improvement has come from shutting down smaller, labor-intensive operators or forcing them into mergers with better-funded state companies.

Major mine accidents in China in recent years include a coal mine flood in eastern Shandong province in August 2007 that left 172 miners dead and a mine blast in northeastern Liaoning province in February 2005 that killed 214 miners.