Beijing - Many people in China's quake-hit Sichuan province fled their home towns and villages overnight after government seismologists forecast a major aftershock measuring between 6 and 7 on the Richter scale, state media said on Tuesday.

Local television and radio broadcast the forecast by the Sichuan seismological bureau of an aftershock on Monday or Tuesday in Wenchuan county, the epicentre of the devastating 8.0-magnitude quake that killed more than 34,000 people on May 12.

The bureau warned the local government and people to be prepared for possible emergencies caused by the new aftershock, the official Xinhua news agency said.

Many people in the provincial capital, Chengdu, tried to leave the city or slept outside in case the aftershock came overnight, the agency said.

Chengdu's main roads were jammed with cars on Monday night and Tuesday morning, especially around petrol stations, it said.

The warning sparked panic in some neighbouring regions, especially Zunyi city in Guizhou province, where many people slept outdoors on Monday night.

More panic followed reports that residents of a rural area of Zunyi saw a mass migration of frogs on Monday, a traditional sign of an impending earthquake, the agency said.

Early Tuesday, a team from Shanghai rescued a manager of a hydropower plant who had been trapped under rubble for 179 hours in Wenchuan's Yingxiu township.

The team had battled for more than 30 hours to free 31-year-old Ma Yuanjiang, feeding him water and glucose through a straw to keep him alive.

Several more survivors were rescued from collapsed buildings on Monday, but nearly 10,000 were still buried under rubble and about 30,000 were listed as missing.

The government last week said it expected the final death toll to reach more than 50,000.

Troops on Monday reached the last 77 villages that had been cut off for about one week since the earthquake, the agency said.

But some roads in 52 townships in Sichuan remained blocked and telecommunications were still not restored to 62 townships, reports said.

The government began three days of national mourning for the earthquake victims Monday and suspended the Olympic torch relay through China.

More than 20 aftershocks measuring 5 or above on the Richter scale have already hit Sichuan since May 12, hampering relief efforts and causing some new casualties.