The magnitude 6.2 quake struck in Gansu’s Jishishan county, about 5km (3 miles) from the provincial boundary with Qinghai. The epicentre was about 1,300km (800 miles) southwest of Beijing, the Chinese capital.
There were nine aftershocks by 10am local time, about 10 hours after the initial quake, the strongest one registering a magnitude of 4.1, a Gansu official said.
Nearly 4,000 firefighters, soldiers and police officers were deployed or on standby as part of the rescue effort.
Emergency authorities in Gansu province also issued an appeal for 300 additional workers to comb through collapsed buildings and for other search and rescue operations.
In Qinghai, officials reported 20 people missing in a landslide, according to Chinese state-owned media.
The earthquake left more than 500 people injured, severely damaged houses and roads, and knocked out power and communication lines, reports said.
It struck just before midnight on Monday near the boundary between the two provinces at a relatively shallow depth of 10km (6 miles), the China Earthquake Networks Center said.
China said the quake had a magnitude of 6.2, while the United States Geological Survey reported the magnitude was 5.9, and the European Mediterranean Seismological Centre said it was a magnitude 6.1 earthquake.
The death toll is the highest since an April 2013 earthquake killed 196 people in southwest China’s Sichuan province.
A 7.9 magnitude earthquake in 2008 was the country’s deadliest in recent years, which killed nearly 90,000 people in Sichuan.