A lake created by the Chinese earthquake which threatens to unleash a devastating flood is still rising despite desperate efforts to drain the waters off safely, Xinhua news agency reported on Sunday.

Troops fired missiles and used dynamite to help blast out a sluice channel to drain off a huge volume of water which has built up behind the mud-and-rock dam at Tangjiashan in the southwestern province of Sichuan.

Landslides blocked the Tongkou River in last month's 7.9 magnitude quake, creating the biggest of more than 30 "quake lakes" formed by a disaster which has already killed 69,000 people.

Worried that the Tangjiashan dam could now burst in a sudden rush, officials have evacuated more than 250,000 people from downstream areas.

Some 600 armed police and soldiers have worked for six days to dig a 475-metre channel to run off water from the lake in Beichuan County.

The lake's water level was 741.82 meters above sea level at midday on Sunday, 1.45 meters higher than the sluice, state-run Xinhua said.

Military engineers have fired missiles to blast boulders in the channel to accelerate drainage, and soldiers have finished building one third of a second channel, said Liu Yongjian, a People's Liberation Army (PLA) officer in charge of the operation.

"We have also prepared underwater blasts to deepen the channels for accelerated drainage," said Liu.

DANGER DOWNSTREAM

Xinhua quoted General Ge Zhenfeng, deputy chief of the General Staff of the PLA, as saying: "Generally speaking, construction of the lake's drainage projects is going well, but the lake remains dangerous for hundreds of thousands of people downstream.

"It will take us a few days to eliminate the potential danger of the lake."

Zhang Ting, head of the Sichuan provincial hydro-meteorological bureau, told Xinhua: "The drainage plus natural leakage of the lake is about 25 cubic metres per second, while the inflow is 4.6 times more than that."

No rain was forecast in the area for Monday, aiding relief efforts.

Rao Xiping, head of the Beichuan hydro-meteorological station, said the lake dam remained stable.

"We have found no obvious expansion of the sluice holes nor fissures in the dam. There is no sign of dam collapse either," said Rao, according to the Xinhua report.

Separately, the State Council Information Office said the death toll from the quake had risen slightly to 69,136 as of midday Sunday, with 17,686 others still reported missing, while 374,061 people had been injured.