Rain, flash floods and mudslides threatened the search for dozens of people still missing on Thursday, days after a strong earthquake rocked mountainous southwest China, killing at least 82.

The magnitude 6.6 quake hit about 43 kilometres (26 miles) southeast of the city of Kangding in Sichuan province at a depth of 10 kilometres on Monday, according to the US Geological Survey, forcing thousands to be resettled into temporary camps.

State broadcaster CCTV said that 46 people died in Ganzi prefecture near the epicentre, while 36 deaths were reported in neighbouring Ya'an city.

More than 270 others were injured while the number of missing remained at 35, CCTV reported without giving more details about the situations of those unaccounted for.

A yellow alert issued by the national weather service -- warning of a "risk of geological disaster" -- was in force until Thursday night, and moderate rain was forecast to continue to Friday with heavy showers in some areas.

"Since the post-earthquake geological conditions are inherently fragile, and the impact of additional rainfall may lead to landslides and mudslides, the local area needs to beware of secondary disasters," China's meteorological administration said.

The People's Liberation Army, paramilitary police, and fire rescue services dispatched more than 10,000 workers to the area, who continued search operations and landslide clean-up efforts in the remote countryside.

Rescuers braved flash floods and landslides caused by aftershocks to relocate villagers from destroyed homes, often having to haul them through mountainous terrain on ropes and stretchers.

CCTV images showed soldiers in military fatigues and orange life jackets using a zip-line to ferry people across river rapids.

"We also waded through the water to get to Xingfu village. The mountain torrents contain rocks... the stones you can't see in the water pose the greatest threat to us," a rescue team member named Tan Ke told CCTV.

"We quickly used ropes to build a human ladder... when we first started wading, the water reached our knees and thighs. By the time we got to a safe place, the flash flood had reached waist level."

Over 22,000 people have so far been moved into 124 temporary sites across Ganzi and Ya'an, the state-owned People's Daily newspaper reported.

The paper said over 21,000 students and staff at a school in Shimian county, where Ya'an is located, were safely evacuated within one minute of the quake.

Nearly 1,800 schools in the area had reopened by Wednesday, it added.

Workers raced to fix hundreds of kilometres of power and optical cables, with communications in affected areas "basically restored" as of Thursday, the China Youth Daily reported.

Local authorities have received over 100 million yuan ($14 million) in disaster relief donations so far, the report said, and the Sichuan government issued an emergency notice requiring local authorities to dish out hardship allowances for affected people.

The quake also rocked buildings in the provincial capital of Chengdu -- where millions are confined to their homes under a strict Covid-19 lockdown -- and in the nearby megacity of Chongqing, residents told AFP.