Rescue workers in northwestern China were racing against time and freezing temperatures to find missing survivors from an earthquake that has killed more than 100 people and injured many more.

The epicenter was centered on Gansu’s Linxia Hui Autonomous Prefecture, which has 2.7 million residents and is roughly 60 miles southwest of the provincial capital, Lanzhou.

The remote location, high altitude and frigid temperatures have made rescue work a particularly difficult challenge. After most earthquakes, the first 72 hours are critical for identifying survivors. In this case, Wang Duo, a team leader of the Gansu Houtian Emergency Rescue Corps, told state media, “the golden hour for rescuing people for this earthquake will be shorter.”

China’s leader, Xi Jinping, called for all-out efforts in the search and relief work, noting the difficulties presented by the high altitude and low temperatures, according to state media.

In Qinghai, the earthquake triggered landslides, and at least 20 people were reported missing, state media said. Water, electricity, transportation and communication systems were damaged in some places. Later Tuesday, state media said electricity supplies in Qinghai and Gansu had fully resumed.

A state-media video clip showed the Qinghai Communist Party chief, the highest official in the province, hugging a crying quake victim and asking the victim to have faith in rescue efforts. Separately, the Lanzhou city government said local police detained two people accused of spreading rumors about strong aftershocks.

The altitude of the immediate vicinity around the earthquake’s epicenter averages more than 9,700 feet, according to state media—nearly twice the altitude of Denver.

Residents of Jishishan, the county in Linxia prefecture that was hardest hit by the earthquake, said it has been snowing there for more than a month, with temperatures falling to between 5 and 10 degrees Fahrenheit at night and many roads covered in snow and ice.

Video footage and photographs provided by state media showed rescue workers pulling out victims in the dark, buildings with collapsed roofs, residents huddled outside under blankets and rubble and loose bricks strewn across the streets.

Ma Zhongliang, a 33-year-old restaurant owner in Dahejia Village in Linxia Prefecture, was getting ready for bed when his room began to shake. “It’s like you’re standing between two trains. Everything is shaking violently,” he said of the tremors, which he said in a phone interview lasted less than 10 seconds.

Ma and his wife crawled under a table to seek shelter and survived unscathed, but his mother was struck by a loose brick and went to a hospital, he said.

Both his restaurant and his home collapsed, he said, along with almost every other building in his village. Most of his 11 family members are now staying at the town center where rescue workers have set up tents and provisional beds and are giving out warm meals of noodles, rice buns and eggs.

Ma helped with rescue efforts throughout the night, trying to find those buried under the rubble, using his cellphone flashlight to illuminate the dark. “Some were alive, some didn’t make it,” he said. Some residents had already been asleep and were thinly dressed, making the subzero temperatures even more dangerous, he said.

Liu Zhenfang, a 35-year-old receptionist at a hotel in Jishishan, roughly 10 miles from the epicenter, said in a phone interview that the tremors were so violent “the dust was shaken off the surveillance cameras.” She, her colleagues and all the guests ran into the street.

The government has dispatched 1,400 rescue personnel to the earthquake zone, with another 1,600 on standby, a local official in Jishishan said on Tuesday.

Many of the rescue workers had arrived by 2:30 a.m., roughly two hours after the quake, said Jishishan resident Ma Aiyoubu, who provided a video filmed in his bathroom, where the water boiler had fallen to the ground.

Other groups of helpers were combing villages, courtyard by courtyard, looking for survivors, state media said.

Yang Zhongxia, a farmer who lives in Qinghai province, 45 miles away from the quake’s epicenter, told state media that he grabbed his grandson and hid him between the bed and stove when the tremors began.

Once the shaking stopped, he and his family got into their car but soon encountered an avalanche of debris triggered by the earthquake. “The sound of it was like that of firecrackers going off,” he said.

The quake was followed by more than 300 aftershocks, state media said, most of which were magnitude 3 or less.

The area is prone to earthquakes, sitting as it does on the northeastern edge of the Tibetan Plateau, near where the Indian and Eurasian Plate meet. Since 1900, three earthquakes with magnitudes above 6 have occurred within 120 miles of Monday’s epicenter, state media said.

China’s large population means even earthquakes in relatively remote areas can cause mass deaths. A 7.9-magnitude quake in 2008 in the southwestern province of Sichuan left more than 87,000 people dead or missing.