State television said the flood on Thursday in the Xinjing Coal Mine in Shanxi province was the biggest accident so far this year in China's disaster-plagued mining industry, which suffers thousands of deaths annually.
Mine managers failed to report the true size of the disaster, saying only five miners were missing, the official Xinhua News Agency reported on Sunday.
"In this sense, the actual situation of the accident was covered up," Xinhua said, citing Gong Anku, head of the Shanxi provincial industrial safety bureau.
Nine managers have been detained, and their boss is in hiding, Xinhua said.
Mine managers drove relatives of missing miners by taxi out of Shanxi to the neighbouring Inner Mongolia region "to prevent them from rioting and speaking to the press", Xinhua said.
Chinese mine managers have used similar tactics after previous accidents, effectively detaining miners' families to compel them to accept financial settlements and promise not to talk to reporters.
A 200-member rescue team was searching for the missing miners, Xinhua said. It didn't say how many were believed to be alive.
The mid-day national TV news showed rescue workers setting up a crane outside the mine and the director of China's national safety agency, Li Yizhong, talking to officials at the scene.
Rescue workers were using nine pumps to drain the mine and were bringing in three more, state television said.
Soaring demand for coal has hit
efforts to improve mine safety
A total of 145 miners were working in the Xinjing Coal Mine at the time of the accident, and 101 escaped, Xinhua said.
But state television said the number of missing might be even higher, because disorderly mine management left it unclear how many were working underground.
The mine was operating at more than 10 times its licensed output level, digging as much coal in one month as it was supposed to produce in a year, state TV said.
China's coal mines are the world's deadliest, with about 6,000 deaths every year in fires, floods and explosions, often blamed on indifference to safety rules and lack of required equipment.
The annual death toll has been unchanged in recent years despite repeated official promises to crack down.
Safety efforts have been complicated by soaring coal prices amid China's booming economic expansion, which encourages local officials to overlook violations in order to maximise revenues.