Chinese officials said an earthquake in a remote mountainous region of the country's southwest has killed at least 357 people and collapsed thousands of buildings.
Officials said more than 1,400 people were injured in Sunday's quake. Many people are still missing.
The quake's epicenter was in Longtoushan in southwestern Yunnan province, at a depth of 12 kilomters, the official Xinhua news agency said.
Ludian County, a densely populated county with nearly 430,000 residents, is located about 366 km northeast of Yunnan's capital, Kunming.
Xinhua said the tremor destroyed 12,000 homes and damaged another 30,000.
The U.S. Geological Survey said Sunday's earthquake had a magnitude of 6.1. Chinese authorities said the magnitude was higher.
A second, 4.1-magnitude quake was registered just 2.5 hours later, 18 km south of Zhaotong City, USGS said.
Ma Liya, a resident of Zhaotong, told Xinhua that the streets there were like a "battlefield after bombardment." She added that her neighbor's house, a new two-story building, had toppled, and said the quake was far worse than one that struck the area in 2012 and killed 81 people.
"The aftermath is much, much worse than what happened after the quake two years ago," Ma said. "I have never felt such strong tremors before. What I can see are all ruins."
Photos on Weibo, China's Twitter-like social media site, showed rescuers searching through flattened buildings and people injured amid toppled bricks.
UN Secretary-General Ban Ki-moon offered "his condolences to the Chinese Government and the families of those killed," according to a statement from his office.
The statement said the UN is ready to "lend its assistance to efforts to respond to humanitarian needs" and "to mobilize any international support needed."
The United States has also expressed condolences and offered help.
"Our thoughts and prayers are with the families of those that lost their lives, those injured or displaced, and all the people of China on this difficult day," the White House said in a statement.
It said that American disaster response officials were in contact with their Chinese counterpart and that the U.S. stood ready to assist.
Xinhua said the government is sending thousands of tents, folding beds, quilts and coats to the affected area. The news agency added that electricity and telecommunications were cut off in the county.
State media announced that 2,500 troops had been dispatched to quake-hit areas late Sunday, joining a team of more than 300 police and firefighters from Zhaotong City, the capital of the prefecture.
News reports said rescuers were still trying to reach victims in more remote towns Sunday night.
Chinese state broadcaster CCTV said the earthquake was the strongest to hit Yunnan in 14 years.
Southwestern China is frequently struck by earthquakes.
In 1970, a magnitude-7.7 earthquake in Yunnan killed at least 15,000 people, and a magnitude-7.1 quake in the province killed more than 1,400 in 1974.
In May 2008, a powerful quake in Sichuan province left nearly 90,000 people dead or missing.
Heavy rain in the vicinity may pose challenges to rescuers, with more downpours forecast in the coming week, according to the China Meteorological Administration.
Some information for this report provided by Reuters and AP.