BEIJING: Rescuers shoveled and hammered at debris on Wednesday, searching for survivors buried under sludge, mud and mining waste in northern China after a landslide that killed at least 56 people, but hopes of finding anybody alive faded. The landslide that plowed into buildings Monday in a valley in Shanxi Province's Xiangfen County also injured 35 others and trapped an unknown number of people under the rubble, local officials said. A preliminary investigation showed that the landslide was caused by the collapse of a dam used as a retaining wall to enclose tailings from an iron mine, said Wang Dexue, deputy head of the State Administration of Work Safety. "It is an illegal company that was using the abandoned dump to get rid of its production waste," Wang said in an interview broadcast on state television. Heavy rains caused the already overloaded dump to breach, Wang said. The state-run news agency Xinhua said the State Council, China's cabinet, will open an investigation into the cause of the landslide. Nine people suspected of being responsible for the incident, including the owner of the mine, were arrested, the news agency reported. A low-rise office building, a market and some houses were knocked down by the rapid surge of mud and mining waste, which formed a wall three stories high and 600 meters, or 1,970 feet, wide, according to media reports. State-run media had initially reported that there were hundreds of people missing, but later cited the authorities as saying the figure could not yet be determined. Xinhua quoted a local government official, Lian Zhendong, as saying that rescuers had searched through 70 percent of the rubble. But local officials said Wednesday they feared that chances of survival were slim. "There were survivors on the first day and on the second day, but from day three, it's very likely that anyone we find in the future will be dead already," said a woman named Dong who heads the public relations department of Xiangfen County. Dong said by telephone that more than 2,000 police, firefighters and villagers were mobilized in the search, but conditions were difficult. "There is mud everywhere," said Dong, who was speaking from the site where excavators and fork-lifts were lifting earth and debris. "It is very hard for the machines to drive through the mud." Also hampering rescue efforts were the rough terrain, poor telecommunications and heavy rainfall, which halted only on Wednesday, Dong said. Like many Chinese officials, she refused to give her full name. The accident underscores two major public safety concerns in China: the failure to enforce protective measures in the country's notoriously deadly mines, and the unsound state of many of its bridges, dams and other aging infrastructure. Xinhua said that several officials, including the local head of the work safety administration, the village party secretary and the village chief, have already been fired for negligence.