Chinese authorities are facing a "race against time" to ensure victims of the deadliest earthquake in years can be sheltered from freezing winter temperatures, a local official told AFP on Thursday.

The quake, which struck just before midnight on Monday on the border between northwestern Gansu and Qinghai provinces, killed at least 135 people. 

The crippling December weather has made the aid operation even more challenging.

"Right now, it's a race against time to meet the needs of the population as quickly as possible, so that people can spend a warm winter in complete safety," Zhou Yongfeng, an official from Gansu's Jishishan county, told AFP.

Swathes of China are experiencing record-breaking cold temperatures, with authorities putting much of the country on alert. 

AFP reporters saw survivors huddling around fires to keep warm, and the government has issued thousands of blue tents to replace improvised shelters built by residents immediately after the quake.

A huge logistics operation has unfolded over the past three days, AFP saw, with thousands of relief workers setting up shelter, food and other facilities for the displaced. 

Zhou, who works in Liugou — a township of about 2,500 households near the epicentre of the quake — told AFP that resettlement was a problem. 

"Makeshift tents are not a long-term approach… But as winters are too cold in northern China, it's not possible to rebuild directly after the disaster," she said. 

"Work can only start in the spring of next year."

Liquefied soil

Almost 1,000 were injured across the two provinces after the shallow tremor, measured at 5.9 by the US Geological Survey, struck. 

The death toll rose on Thursday, state news agency Xinhua said, as rescuers continued to search for victims buried alive on Tuesday in Zhongchuan township in Qinghai.

Twelve people there remain missing after a "sand boil" — a phenomenon that can occur during an earthquake when soil liquefies and forces sand and water out of the ground — according to Xinhua.

The quake was China's deadliest since 2014, when more than 600 people were killed in southwestern Yunnan province.

At the Jishishan County People's Hospital in Gansu, doctors attended to survivors with mild injuries on Thursday, administering intravenous drips and examining X-rays.

The hospital buildings themselves had been visibly damaged by the quake. 

"I really want to go home," one patient, a middle-aged woman waiting to receive surgery on her injured leg, told AFP.

"But my place has been destroyed, so I wonder where I can go," she said.

"People are still worried about the aftershocks," another Jishishan county official told AFP.

"They can't sleep well because there is no safe place."