XIANGNING, China —The first group of rescuers and divers entered a flooded Chinese coal mine where 153 workers have been trapped for almost a week, but returned within hours Saturday and called the situation underground “very difficult.” There were no further signs of life after tapping was heard the previous day.

The divers said black, murky water was complicating efforts to reach the site where rescuers hope miners are still alive, state-run China Central Television reported.

The next step in the rescue plan was under discussion and wasn’t expected until today, said Wen Changjin, an official with the news center set up at the mine in the northern province of Shanxi.

Television footage Friday showed rescuers tapping on pipes with a wrench, then cheering and jumping after hearing a response — the first sign of life since the mine flooded last Sunday. They lowered pens and paper, along with packs containing glucose and milk, down metal pipes into the mine.

But nothing more had been heard as of Saturday afternoon, Wen said. Rescuers also lowered a listening device down the drill pipe to the pit, hoping to hear voices or other sounds of life, but heard nothing, the official Xinhua News Agency reported.

It was not immediately clear what risks rescuers were taking by entering the Wangjialing mine. But, 3,000 rescuers were working nonstop to pump out water that poured in last Sunday when workers digging tunnels broke into an abandoned shaft.

Wen said the water level underground had dropped by about 15 feet as of noon Saturday. But experts said it could take days to reach the miners — and their survival depended on whether they had decent air to breathe and clean water to drink.

“They’re doing probably the only thing they can do, which is to pump water as fast as they possibly can,” David Feickert, a coal mine safety adviser to the Chinese government, said Friday.

The 153 workers were believed to be trapped on nine different platforms in the mine, which was flooded with the equivalent of more than 55 Olympic swimming pools, state television reported.

A preliminary investigation found that the mine’s managers ignored water leaks from the abandoned mine before the accident, the State Administration of Work Safety said.

China’s coal mines are the world’s deadliest. Accidents killed 2,631 coal miners in China last year, down from 6,995 deaths in 2002, the most dangerous year on record, according to the State Administration of Coal Mine Safety.