Beijing  - China evacuated tens of thousands of people in the quake-hit south-western province of Sichuan on Tuesday, as troops battled to dig through a natural dam that threatened to burst and flood the area.

State media said more than 70,000 people were evacuated early Tuesday in Sichuan's Beichuan county and that another 80,000 would move to safer areas by midnight.

More than 100 military engineers set off for the dam in Sichuan's Tangjiashan area on Tuesday to join hundreds of soldiers already working on water diversion plans.

The troops and excavators had to be dropped by helicopter since a huge landslide on May 12 blocked a river and cut all roads to the area.

They were trying to construct a 200-metre sluice to drain the lake, which had risen to just 26 metres below the top of the lowest part of the dam by Monday.

The water in the lake rose by another 1.8 metres on Tuesday and was expected to continue rising by about 2 metres per day.

The formation of the lake and 34 similar ones has brought new fears to hundreds of thousands of survivors of the devastating 8.0-magnitude earthquake that is thought to have killed at least 80,000 people.

The government on Tuesday said the confirmed death toll had reached 67,183, with 20,790 still missing and 15 million evacuated.

The Tangjishan lake held an estimated 130 million cubic metres of water on Monday, the agency quoted Liu Ning, the chief engineer from the Ministry of Water Resources, as saying.

Three emergency plans were drawn up for digging the sluice, depending on weather conditions and how quickly the troops were able to work, a military official told the agency.

An aftershock measuring 5.4 on the Richter scale also shook the area on Tuesday afternoon, one of the more powerful of thousands of aftershocks to hit the area since May 12.

A 6.4-magnitude aftershock killed at least eight people and injured scores on Sunday. (dpa)