Chendu -- China struggled to keep roads open to provide a lifeline for quake survivors, while the government said Wednesday that rebuilding after the disaster would be "arduous."

The magnitude 8.0 quake that struck May 12 sent dirt and rocks tumbling into valleys, blocking roads to hinder relief efforts and clogging rivers that have developed into fast-rising lakes.

"We are racing against time to repair damaged infrastructure," said Mu Hong, a deputy director at the National Development and Reform Commission, the country's top economic planning body, adding that some roads were only reopened on a temporary basis.

Workers look into temporary housing being built for residents affected by an earthquake in Dujiangyan, west of Chengdu, Sichuan Province May 22, 2008. Millions of people became homeless after a massive earthquake hit the province on May 12. [Agencies]

"The high risk of mudslides and landslides makes our efforts more difficult," he said.

Rebuilding infrastructure is just a part of the recovery effort that government officials said earlier would take three years in hard-hit Sichuan province.

"Due to the immense magnitude of loss resulted from the quake, production recovery and reconstruction of the quake-hit region will be arduous in the near future," the commission said in a statement.

In the disaster zone, 158,000 people have been evacuated and dozens of villages emptied in case the earthquake-created Tangjiashan lake bursts before soldiers and engineers can drain it.

Troops used explosives to clear debris and helicopters to airlift heavy moving equipment to dig drainage channels from the lake, located about 2 miles (3.2 kilometers) above the devastated town of Beichuan.

People take part in an evacuation drill in Jiangyou, Sichuan province May 27, 2008.  [Xinhua]

Forty machines, including excavators, were at the site, which was unreachable by road, and hundreds of troops are working around the clock to dig the channel, the official Xinhua News Agency reported.

Yang Hailiang, the official heading the operation, said the teams were making good progress thanks to clear weather, and that they were one-third of the way through the job, Xinhua said.

At the riverside Tongkou village downstream from the lake, residents have been moved to a camp up the hill but were returning each day to tend to their fields.

"If the water comes down from the burst dam, somebody will launch a fireworks signal to give us warning so everybody can run uphill," said villager Wang Hongyun. "Without seeing the warning, we will keep on gathering our crops."

Premier Wen Jiabao told a meeting of the State Council, China's Cabinet, that handling the danger from the swelling lakes was the "most pressing task" in the disaster recovery effort.

The government has allocated 200 million yuan (US$28.6 million) to deal with the swelling lakes, Xinhua said. Of 34 lakes created by the earthquake in the mountainous province, 28 were at risk of bursting, according to the agency.

Meanwhile, the number of confirmed deaths from the quake climbed toward an expected toll of more than 80,000. The State Council said Wednesday that 68,109 people were killed, with 19,851 still missing.