The 7.0 magnitude earthquake hit the Sichuan province at just after 8am local time (midnight GMT) near Ya’an city – home to around 1.5 million people.
State television reported that at least 156 people had died, whilst 5,500 are said to be injured, as buildings collapsed and landslides were triggered.
The village of Longmen in the mountainous Lushan county was hit particularly hard, with authorities saying nearly all the buildings had been destroyed and state television showing footage of soldiers digging through rubble.
China’s seismological bureau measured the quake at a magnitude of 7.0 and the U.S. Geological Survey at 6.6.
The government has sent thousands of soldiers and workers to the area, as well as excavators and other heavy machinery, tents, blankets and other emergency supplies.
Premier Li Keqiang flew to Ya’an to direct rescue efforts, and he and President Xi Jinping ordered officials and rescuers to make saving people the top priority, state television agency Xinhua said.
Roads were blocked for several hours after the quake, forcing the military to survey the damage by the air. Aerial photos released by the military and shown on state television showed individual houses in ruins in Lushan and outlying villages flattened into rubble (see picture, above).
The roofs of some taller buildings appeared to have slipped off, exposing the floors beneath them.
China Earth Administration said there had been at least 35 aftershocks, including at least two of magnitude 5.0 or higher.
The earthquake struck in the same area devastated by a magnitude 7.9 quake which hit in May 2008, leaving more than 90,000 people dead or missing and presumed dead in one of the worst natural disasters to strike China in recent decades.