Hundreds of miners, police and others were involved in the operation, but officials warned people to expect the worst in what will likely be one of the biggest Chinese mining disasters in recent years.

"We are pumping the water out of the wells... but hopes of anyone surviving are very slim," State Administration of Work Safety spokeswoman An Yuanjie told AFP.

Torrential rains on Friday led to a river bursting its banks, sending water cascading into the mines that sit 10 kilometres (six miles) apart in the city of Xintai, in eastern China's Shandong province.

Over 750 miners were underground when the water swept into the Zhangzhuang mine. Although many managed to escape, 172 were trapped and have not been heard from since.

In the other accident, nine people were trapped at the Minggong coal mine, and are also feared dead.

The twin disasters have once again thrown the spotlight on China's coal mining industry, regarded as riddled with corruption and the most dangerous in the world.

At the Zhangzhuang mine, officials said water almost completely filled the 860-metre (2,840-foot) pit on Friday.

About 24 hours after the flooding, water was still as high as 20 metres below the surface, leaving the trapped miners with only the slimmest hopes of having found an air pocket.

At the mouth of the mine, a three-by-three-metre hole, dozens of people were Monday busy preparing pipes to pump out water.

Specialists were assembling pumps and pipes which, once in place, could start sucking out the remaining water, paving the way for the actual search and rescue.

"This is some of the best, most advanced equipment in China," said Ba Yanping, an official of the China Coal Group.

But Bu Changsheng, an expert in hydraulic engineering called in for the disaster, suggested the wait for news could be a long one.

"It will be two days before the piping has reached the bottom of the mine," he said. "All we can say is that we're doing all we can, 100 percent, to rescue the missing."

Meanwhile, other coal miners continued to shore up dykes to stop more water pouring in.

"We are incredibly busy. Last night I got one or two hours' sleep. The night before, no sleep at all," a colleague of the trapped miners surnamed Niu said as he took a quick break from his work.

With tensions high, scuffles broke out on Sunday between relatives and security forces at the Zhangzhuang mine.

A crowd of 200 people, angry at the lack of information, toppled an iron fence at the south gate of the mine early in the day as rumours swirled that rescue efforts had been called off.

On Monday, the two main gates were virtually empty of people, and security also appeared to have been scaled down significantly.

If all the miners are indeed dead, the Xintai tragedies will be the worst reported coal mining disaster since an explosion at a colliery in Liaoning province in 2005 claimed 214 lives.

More than 4,700 coal miners died last year, according to official figures, but independent labour groups put the real toll at up to 20,000 annually, saying many accidents are covered up.

Central government authorities have repeatedly complained about mine bosses and local officials colluding to put profits and economic growth ahead of workers' safety.

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