The 6.5-magnitude quake struck in the sparsely-populated north of Sichuan, the US Geological Survey said.
Some reports suggest the death toll could be much higher. The epicentre was close to an area popular with tourists.
Sichuan province is prone to earthquakes. More than 70,000 people were killed in a quake in 2008.
The quake struck at around 21:20 (13:20 GMT) some 300km (180 miles) north of the provincial capital Chengdu, and was 10km deep.
Photos showed damage to buildings, including a hotel, in Jiuzhaigou, home to one of China's most famous nature reserves and a Unesco World Heritage site.
A restaurant owner in the town said this quake felt stronger than the 2008 tremor, though there is no suggestion yet that the death toll could reach anywhere near the levels caused by that disaster.
Tang Sesheng told the AFP news agency that many people had fled buildings in Jiuzhaigou county - which includes a national park - and were taking refuge in the main square.
"People didn't dare grab anything like money or clothes - we just all ran outside right away," she said.
Gwendolyn Pang of the Red Cross Society of China said it would take time to learn the extent of the damage and number of casualties.
"Communications lines and electricity are disrupted and people are no doubt shocked and scared," she said.
China's National Commission for Disaster Reduction, quoted by AFP news agency, said as many as 100 people may have been killed and 130,000 homes damaged.
Some reports in the Chinese media said tourists were among the dead and injured.
President Xi Jinping called for "all-out efforts to rapidly organise relief work and rescue the injured people", state news agency Xinhua reports, and fire officers and soldiers were being deployed from nearby areas.
Shaking was felt in Chengdu and in Xian, home to the Terracotta Warriors, some 700km (430 miles) away.
An earthquake has killed at least five people and injured more than 60 in China's south-western province of Sichuan, officials say.