A swollen "quake lake" in one of the worst hit areas in China's devastating earthquake has topped the country's agenda of relief work.

The Tangjiashan quake lake formed by the landslide following the May 12 earthquake near Beichuan County in southwest China's Sichuan Province is seen on Monday, May 26, 2008. Chinese officials rushed Tuesday to evacuate people in the path of potential floodwaters building up behind a quake-spawned dam as soldiers carved a channel to try to drain away the threat.

In a phone call on Monday night, Chinese President Hu Jintao told Vice Premier Hui Liangyu, who were in southwestern Sichuan province to oversee the quake relief work, that the relief task force must make sure no serious problems occur in the emergencies.

"We must put people first and the priority is to protect their lives," he said.

Chinese Premier Wen Jiabao said in Beijing on Tuesday the relief headquarters will evacuate residents from the area downstream of the lake and at the same time, try to drain the water. "We must well prepare and do the two parts of work side by side."

The lake, at Tangjiashan of Beichuan County in Mianyang City, Sichuan Province, was formed by landslides that blocked the Jianjiang River after the May 12 quake.

It was holding 130 million cubic meters of water, said Liu Ning, Ministry of Water Resources chief engineer, who is at Tangjiashan to oversee the diversion work.

Its water level was 727.09 meters on Tuesday, only 24.21 meters below the lowest part of the barrier, according to Mianyang City Quake Control and Relief Headquarters.

Hui flew to the lake on Tuesday morning to check the situation on ground. When he returned to Mianyang, he called a meeting to discuss plans to defuse the danger imposed by the quake lake.

"The Tangjiashan quake lake should be our most urgent task. It is threatening millions of lives in the area downstream and any negligence will cause new disasters to people who have already suffered the quake," he told the meeting.

The diversion work has been on the track, he said, "We will well prepare for the worst situation, taking account of any possible difficulties in draining the lake and evacuating the people".

So far, more than 70,000 people in Mianyang City have been relocated.

In total, 158,000 people from 169 communities in 33 townships of Mianyang will have to move from their homes if one third of the lake volume bursts its banks, according to an emergency plan drawn up for the contingency.

Hui asked the headquarters to perfect the contingency plans, check every detail and push ahead the work in an orderly fashion.

He stressed enhanced monitoring of the lake's situation.