Rescuers continued to work all-out on Friday in the hope of reaching 16 miners who became trapped in a flooded colliery pit in central China's Hunan province 40 hours ago.

As of 11 a.m., rescuers had removed three huge rocks that were blocking a major passageway in the shaft, but were yet to find the miners, said a spokesman with the emergency rescue headquarters in Leiyang city.

The miners were trapped in a pit of Qielichong colliery in Sandu township following a mine flood at 6 p.m. on Wednesday. Of the 40 people working in the pit, 24 managed to escape.

But the accident was not reported to the local government until 6:30 a.m. on Thursday, which delayed the start of the rescue operation by almost 12 hours, the spokesman said.

Four teams of rescuers were sent to the scene on Thursday morning. They drained the pit of flood water and resumed ventilation in the shaft on the same day, he added.

The rescuers have been taking turns to enter the shaft for search and rescue every six hours. Medical workers are standing by waiting to provide first-aid to survivors.

The mine owner, Liu Yaping, is under police custody.

The cause of the flood is still unclear.