Beijing - Officials and troops have drilled 1.3 million people in south-western China's Sichuan province to flee within four hours if a lake created by a major earthquake is about to burst its banks, state media said on Wednesday.

About 158,000 people were evacuated from high-risk areas of Sichuan's quake-devastated Mianyang city and the remaining residents were "kept well-informed of the emergency evacuation plans through repeated drills and public announcements," the official Xinhua news agency quoted an official as saying.

The drills included learning the routes for evacuation, directions to safe areas and locations of temporary shelters, said Tan Li, the head of Mianyang's branch of China's ruling Communist Party.

"The efforts are aimed at getting all the 1.3 million residents on the move within four hours in case the quake lake bank fully opens, and zero deaths in the process of evacuation," Tan was quoted as saying.

Thousands of soldiers, armed police and security officers were on standby and planned to go door to door to evacuate people if the lake was about to flood the area, he said.

The government said the confirmed death toll from the May 12 earthquake, whose epicentre was close to Mianyang, had risen to 68,109 by Wednesday.

A total of 19,851 people were still listed as missing, about 15 million were evacuated and another 35 million were homeless.

Helicopters have airlifted hundreds of troops and several excavators to the lake at Tangjiashan above Mianyang's Beichuan town, since the only road through the area was cut by the massive landslide.

The troops are digging a sluice to let water out of the lake, which held an estimated 130 million cubic metres of water on Monday.

Earlier reports said that the sluice and a water diversion channel should be finished by June 5, but that troops had prepared several contingency plans in case conditions worsened at the lake.

Yang Hailiang, one of the leaders of the emergency work at the lake, told the agency that one-third of the sluice was finished by Wednesday.

The formation of the lake and 34 similar ones in Sichuan have brought new fears to millions of survivors of the devastating 8.0- magnitude earthquake. (dpa)