1.3 mil flee China quake lake

There were no immediate reports of new damage or injuries from Thursday's tremor, which the US Geological Survey recorded in the region at the relatively shallow depth of 10km (six miles).

"Now it's a critical moment for the Tangjiashan quake lake, and the most important thing is to ensure there is no casualty of the people," Mr Wen, on his third trip to the disaster zone, was quoted as saying by the official Xinhua news agency.

Water levels at Tangjiashan had risen to 739 metres (2,440ft) above sea level and the chances of it bursting were increasing, Xinhua said.

Plans are in place to quickly evacuate an estimated 1.3m people who live in the surrounding area if the lake bursts.

More than 250,000 people downstream have already been moved to higher ground.

The level of the lake - which is on the Jian River just above the quake-ravaged town of Beichuan - is still rising, although water has begun seeping out through the debris.

The threat posed by more than 30 quake lakes formed during the earthquake has become one of the most pressing issues in the aftermath of the quake.

Tangjiashan lake -- One of 35 lakes formed after landslides triggered by the quake blocked rivers in the mountains. Tangjiashan lake, which sits on the Jianjiang River, a local waterway, is 3.2 km from the seat of the hard-hit Beichuan County. It is inaccessible by road and can only be reached by foot or air.

    Evacuation plans -- There are three plans to move survivors if necessary. The target is zero deaths, according to Tan Li, Mianyang City Communist Party chief and also chief of its Quake Control and Relief Headquarters. In the first instance, 158,000 people will have to relocate if one-third of the lake breaches its banks. Actually, more than 250,000 people in Mianyang City have already been relocated.

    Two other plans require the relocation of 1.2 million people if half the lake volume is released or 1.3 million if the barrier fully opens.

    Water diversion channel -- A 475 meter channel was cut into the Tangjiashan lake barrier by 620 armed police and engineers over six days and nights. The cubical channel is 12 meters deep and 7 meters wide upstream and in the middle but becomes larger downstream. Most of the workers have already left the site. A dozen police stayed behind to monitor the situation.