Rainfall on early Thursday has increased the difficulty of operations to pump out water from two flooded coal mines in East China's Shandong Province to reach 181 miners that have been trapped for 13 days.

Latest information from the rescue operation headquarters said that it started to rain in Xintai at 2 am on Thursday, but stopped around 8 am. The amount of rainfall reached 18.5 mm.

"The sudden rainfall has adversely affected the rescue efforts, but the operation will go on anyway," said an official in charge of the rescue operation.

Flood water swept through a 65-meter wide breach in the Wenhe River levee on August 17, inundating the Huayuan and Minggong mines, leaving 181 people trapped underground.

Chinese water resources specialists have blamed the disaster largely on heavy rain and inadequate flood prevention facilities.

Eleven pumps are busy working near the mines, of which eight are installed at Daqiao ventilation passage of Huayuan Coal Mine and capable of piping out 6,000 cubic meters of water per hour, according to Wang Baoshan, who is overseeing water pumping operation at the two coal mines.

One more water pump that was trucked in from Central China's Henan Province is still under installation at Huayuan coal mine and would be put into service on Thursday.

By 6 am on Thursday, water level in the shaft of Huayuan coal mine dropped to 51.3 meters, 41.3 meters down from the highest level. But rescuers have to lower the water level by another 81.70 meters to reach the 172 trapped miners.

In the nearby Minggong coal mine, water level lowered to 51.45 meters.