The earthquake Saturday morning triggered landslides and disrupted phone and power connections in mountainous Lushan county five years after a devastating quake wreaked widespread damage across the region.
The village of Longmen was hit particularly hard, with authorities saying nearly all the buildings there had been destroyed in a frightening minute-long shaking by the quake.
In nearby Ya'an town, where aftershocks were felt nearly a day after the quake, residents sat in groups outside convenience stores watching the news on television sets. Fourteen-year-old Wang Xing sat with her family on chairs by the roadside in the cool night air, a large blanket on her lap.
Wang and her relatives decided to spend the night in their cars. "We don't feel safe sleeping at home tonight," said Wang, a student. She said the quake left tears on the walls of her family's house. "It was very scary when it happened. I ran out of my bed and out of the house. I didn't even have my shoes on."
Along the main roads leading to the worst-hit county of Lushan, ambulances, fire engines and military trucks piled high with supplies waited in long lines, some turning back to try other routes when roads were impassable.
Rescuers were forced to dynamite boulders that had fallen across roads to reach Longmen and other damaged areas lying farther up the mountain valleys, state media reported.
Chinese Premier Li Keqiang arrived Saturday afternoon by helicopter in Ya'an to direct rescue efforts, the official Chinese news agency Xinhua reported.
"The current priority is to save lives," Li said, after visiting hospitals, tents and climbing on a pile of rubble to view the devastation, according to Xinhua.
The China Earthquake Administration said at least 160 people had died, and more than 6,700 were injured. At least 96 people were killed in Lushan, and in the jurisdiction of Ya'an, which administers Lushan, 19 people were reported missing, the administration said.
The quake - measured by the earthquake administration at magnitude-7.0 and by the U.S. Geological Survey at 6.6 - struck the steep hills of Lushan county shortly after 8 a.m., when many people were at home, sleeping or having breakfast.
The quake's shallow depth, less than 13 kilometers (8 miles), likely magnified the impact.
Lushan, 115 kilometers (70 miles) west of the provincial capital of Chengdu, reported the most deaths, but there was concern that casualties in neighboring Baoxing county might have been under-reported because roads were blocked and power and phone services cut off.
It rained Saturday night, slowing rescue work, with forecasts predicting more rain in the next several days. The China Meteorological Administration warned of possible landslides and other geological disasters.
Tens of thousands of people moved into tents or cars, unable to return home or too afraid to go back as aftershocks continued to jolt the region.
Lushan, where the quake struck, lies where the fertile Sichuan plain meets foothills that eventually rise to the Tibetan plateau and sits atop the Longmenshan fault.
It was along that fault line that a devastating magnitude-7.9 quake struck on May 12, 2008, leaving more than 90,000 people dead or missing and presumed dead in one of the worst natural disasters to strike China in recent decades.
"It was just like May 12," Liu Xi, a writer in Ya'an city, said via a private message on his account on the Twitter-like Weibo service. "All the home decorations fell at once, and the old house cracked."
The official Xinhua News Agency said the well-known Bifengxia panda preserve, which is near Lushan, was not affected by the quake. Dozens of pandas were moved to Bifengxia from another preserve, Wolong, after its habitat was wrecked by the 2008 quake.
As in most natural disasters, the government mobilized thousands of soldiers and others, sending excavators and other heavy machinery as well as tents, blankets and other emergency supplies. Two soldiers died after their vehicle slide off a road and rolled down a cliff, state media reported.
The Chinese Red Cross said it had deployed relief teams with supplies of food, water, medicine and rescue equipment to the disaster areas.
Aerial photos released by the military and shown on state television showed individual houses in ruins in Lushan and outlying villages flattened into rubble. The roofs of some taller buildings appeared to have slipped off, exposing the floors beneath them.
The earthquake administration said there had been at least 712 aftershocks, including two of magnitude-5.0 or higher.
"It's too dangerous," said a person with the Weibo account Chengduxinglin and with a Lushan geotag. "Even the aftershocks are scary."
While rescuers and state media rushed to the disaster scene, China's active social media users filled the information gap. They posted photos of people fleeing to streets for safety and of buildings flattened by the quake. They shared information on the availability of phone services, apparently through data services.