The swollen lake in Tangjiashan, formed after a quake-triggered landslide blocked the Jianjiang river, has become one of the most pressing issues in the aftermath of the Sichuan quake.

The authorities yesterday issued fresh warnings of flooding, with the water level rising 90cm in 24 hours. Seepage was already occurring, Xinhua news agency reported.

Further complicating the problem was a magnitude 5.3 aftershock which jolted Qingchuan county yesterday - one of more than 10,000 that have hit the disaster zone.

The frequent aftershocks have exacerbated the flood threat by sending waves crashing against the mud and rock blocking the river.

Officials have pinned their hopes on a channel dug by soldiers last week and designed to drain enough water to keep the lake from bursting its banks.

An estimated 1.3 million people live in areas that could be inundated if the plan does not work.

Mr Wen, who arrived at the Tangjiashan lake yesterday, said it was crucial to ensure there were no casualties from any potential floods.

The official death toll from the May 12 quake has risen to 69,127, with 17,918 more missing, China said yesterday.

Many storefronts in Mianyang city, which is downstream from the lake, were sealed and sandbagged. Red stripes spray- painted on trees at a height of about one metre showed the expected water level should the lake burst.

On a road leading to the town of Qinglian near the lake, a kilometre-long line of army trucks was parked, many loaded with olive-green boats, others with portable bridges.

Inside Qinglian, row after row of apartment buildings in the potential flood zone were abandoned, and the residential areas were sealed off with police tape.

'If it's not the earthquake, it's the flood. But if they order us to go, we'll go,' said Ms Liao Guangmei, a 60-year-old woman left homeless by the quake.

But another resident who gave her surname as Li said she was not going anywhere.

'We already had the big earthquake. We are not afraid of aftershocks.'

AGENCE FRANCE-PRESSE