A magnitude-7.0 earthquake struck Jiuzhaigou county in Sichuan province at 9:19 pm on Tuesday, killing at least five people and leaving dozens injured, Xinhua News Agency reported.
All of those killed were reported to be tourists.
The epicenter was at a depth of 20 kilometers in Jiuzhaigou and the Aba Tibetan and Qiang autonomous regions.
Jiuzhaigou national park is in the area and is a popular tourist spot known for spectacular waterfalls and karst formations. Each year, millions of tourists visit.
The area has been hit by frequent aftershocks.
The China Earthquake Administration declared the highest level of the four-tiered emergency response system for earthquakes, and dispatched officers to the region to deal with emergencies.
"Our departments, including the emergency and rescue centers as well as subbureaus in the provinces of Sichuan, Gansu, Qinghai, Shaanxi and the Ningxia Hui autonomous region, have been all standing by and asked related workers to be on duty, monitoring aftershocks, collecting information and making evaluations of possible disasters," the administration said on its official website.
Police in Jiuzhaigou had reached the epicenter to maintain order in the area, said the Armed Police Force's Sichuan Provincial Corp. Other forces around the area also were standing by.
The PLA Daily reported the epicenter is nearly 60 kilometers from the county's downtown, and the telecommunications in the area were temporarily shut down after the quake.
The province's Party chief, Wang Dongming, asked all governmental departments to stand by and dispatched a work team to lead the rescue. He said the priority is to reduce any deaths or injuries and prevent post-quake damages.
Sangey, a worker at the popular Jiuzhaigou tourist site, told Xinhua by phone that some houses in the scenic spot had collapsed or had cracks, and authorities were organizing young people to help evacuate residents.
Li Changyong, head of the Jiuzhaigou county health and family planning bureau, said the quake was strongly felt in the county seat, 35 km from the epicenter, and many residents rushed outside.
Li told Xinhua that he saw no building collapses in the county seat and had learned of no immediate reports of deaths or injuries.
Tremors were felt in the provincial capital of Chengdu and as far away as Xi'an, capital of Shaanxi province, according to media reports.
A quake in Wenchuan county, Sichuan, on May 12, 2008 killed almost 70,000 people.
Xinhua contributed to this story.