More than 12,000 houses collapsed and 30,000 were damaged in the quake zone in the southwestern province of Yunnan, China's official news agency Xinhua said.
Soldiers stretchered the injured away from the scene in the immediate aftermath, one carrying an elderly man on his back another a child in his arms, with residents fleeing in terror as aftershocks hit. Rescuers rushed victims to local hospitals and as dawn broke Monday continued to pick through the rubble of destroyed homes in a desperate search for survivors.
Images on social media showed painstaking attempts to extricate residents from the rubble of their homes, while reports said heavy rains were hampering rescue efforts. In Ludian county, the worst-affected area, Xinhua said its reporters "saw drenched survivors sit along the muddy roads waiting for food and medication. Some half-naked survivors were quivering in the rain".
A total of 7,000 emergency personnel, including 5,000 soldiers, police and firefighters had been mobilised, Xinhua said Monday, and Premier Li Keqiang was heading to the scene. Equipment brought to the area included life detection instruments and excavating tools.
"They are also battling the continual downpour that has brought down the temperature in the remote area and made shortages of food and medicine even more pernicious," Xinhua added.
Volunteers from across China were heading to Yunnan to assist. At the airport in the provincial capital Kunming, one group were discussing how to reach the worst hit areas. "It is our duty to help," one told AFP.
A total of 381 people had been killed by the tremor, with 1,801 injured, according to China's Ministry of Civil Affairs.
Users of China's Twitter-like Sina Weibo expressed sympathy for the victims, posting images of candles and crying faces. "May the dead rest in peace and the living be strong," read one typical comment.
Scene 'like a battlefield'
The US Geological Survey (USGS) reported the quake at a magnitude of 6.1 and said it struck at a relatively shallow depth of 10 kilometres (six miles).
"Too many buildings were damaged and we are collecting data on deaths and injuries," Xinhua quoted local official Chen Guoyong as saying in Longtoushan, the township at the epicentre.
State television broadcast footage of people running from their homes and gathering in the streets, as witnesses described the devastation on social networks.
A Ludian resident described the scene as resembling a "battlefield after bombardment", telling Xinhua: "I have never felt (such) strong tremors before. What I can see are all ruins."
Volunteer Ma Hao, a college student who was helping to carry the injured out of the collapsed buildings in Longtoushan, described a race to pull the living from the rubble that left little time for the dead. "We had no time to take care of the bodies. We need to help those alive first," he told Xinhua.
Electricity and telecommunications have been cut across the area and 57,200 residents need to be transferred to safe areas, Xinhua reported. Ludian has a population of nearly 266,000 and sits more than 300 kilometres north of the provincial capital Kunming.
A spokesman for UN chief Ban Ki-moon said the secretary-general was "saddened by the loss of life", while the White House National Security Council also offered condolences, and said the United States "stands ready to assist".
Chinese state media put the magnitude of the first earthquake at 6.5, citing the China Earthquake Networks Center. Southwest China lies where the Eurasian and Indian plates meet and is prone to earthquakes. In 1974, a 6.8-magnitude quake in the same area killed more than 1,500 people.
In September 2012, 80 people were killed when twin earthquakes struck the mountainous border area of Yunnan and Guizhou. An 8.0-magnitude quake in May 2008 rocked Sichuan, which neighbours Yunnan, killing tens of thousands of people and flattening swathes of the province.