BEIJING, May 12 (Xinhua) -- A senior Chinese seismologist on Monday warned residents in earthquake-affected areas in southwest China that aftershocks could be just as devastating as the main tremor.

    "A big earthquake could release most, but not all of the underground energy, and its aftershocks may cause natural disasters," said Zhang Guomin, a research fellow with the China Seismological Bureau.

    Generally speaking, aftershocks were weaker than the main earthquake, but as many buildings were already damaged, the aftershocks could tear them down, he said.

    With its epicenter in Wenchuan County in Sichuan Province, the earthquake occurred at 2:28 p.m. Monday. Measuring 7.8 on the Richter scale, it was the first in the province above 7 since 1976.

    "Wenchuan is prone to earthquakes as it is on a major fault line -- the south-north fault line that runs from Yunnan to Ningxia," said Zhang.

    The county was also on a small fault line known as Longmen mountain earthquake belt.

    Rescue teams and relief workers, including 5,000 soldiers and police forces from the Chengdu Area Military Command of the People's Liberation Army, have been dispatched to quake-affected areas.