HEGANG, Heilongjiang - No progress has been reported after three days of rescue efforts for 13 miners trapped in a flooded coal pit in Northeast China's Heilongjiang province, local authorities said late Thursday.

Rescuers finally drilled into the shaft Thursday, only to find the location was wrong, said Gui Laibao, deputy chief of State Administration of Coal Mine Safety.

He said the miscalculation was due to old hydraulic mining techniques prevalent in the area 20 years ago.

"Rescuers were unable to work out the exact location of the flood. The old mining technology changed the underground geological data and the maps used by the rescuers were misleading, " said Gui.

Gui said he hoped two new holes drilled Thursday night would hopefully reach the right location.

It was difficult to drill through the shaft as there were more rocks than coal.

Meanwhile, several sources of flood water have converged underground, slowing down the pumping process.

The emergency rescue headquarters had sent more powerful pumps, hoping to pump out flood water faster, said spokesman Wang Kuiyuan.

Wang said the emergency rescue headquarters are keeping the miners' families informed of the rescue progress on daily basis. "We're doing our best to ensure transparency and comfort them as much as we can."

He said family members were becoming desperate now that the 72-hour golden period for rescue had ended.

Flood inundated the Xuxiang Colliery in Hegang's Xing'an district at around 5 pm Monday, trapping 15 miners. Two of them were confirmed dead, but the whereabouts was unknown for the remaining 13.

Hegang is a major coal producer. Xuxiang Colliery is privately owned, with an annual output of 150,000 tonnes.

Wang said mine production had been suspended for a safety overhaul when the accident happened. "The workers were down there for maintenance instead of mining."

He said the accident was caused by a mud-rock flow, which was the aftermath of recent downpours.