Thousands of emergency workers, including soldiers, rushed to reach the affected zones in the hilly region, and Chinese Premier Li Keqiang traveled to the area from Beijing, state media reported.
The death toll rose steadily through the day. It currently stands at 113, with more than 3,000 people injured, the China Earthquake Administration said, according to state broadcaster CCTV.
Xu Mengjia, the Communist Party chief of Ya'an, the city that administers the area where the quake struck, told CCTV that because of landslides and disruption to communications, determining the total number of casualties may take some time.
The quake struck just after 8 a.m. local time about 115 kilometers (70 miles) away from the provincial capital, Chengdu, at a depth of around 12 kilometers, according to the U.S. Geological Survey. There was conflicting information about the earthquake's strength, with the USGS putting the magnitude at 6.6 and the China Earthquake Networks Center gauging it at 7.0.
It was followed by a series of aftershocks, some of them as strong as magnitude 5.1, the USGS said.
Authorities have responded by sending rescue workers to the area around the epicenter, briefly halting flights at the airport in Chengdu and suspending high-speed rail operations, state media reported.