Chinese rescuers raced Friday to find the last worker trapped underground in a flooded coal mine after pulling the rest of the group free, as authorities vowed to crack down on illegal operations that have sprung up in response to price surges.

The group of 21 were trapped when the mine flooded late Wednesday in Xiaoyi city, in northern China's coal-producing Shanxi province, prompting a huge recovery effort.

Hundreds of rescuers have been dispatched to the mine where three pumps were draining the water.

State broadcaster CCTV said a narrow and concealed entrance to the illegal mine had hampered rescue efforts, as well as a lack of a proper map of the site.

Rescuers managed to lift twenty miners to the surface by early evening as efforts to save the remaining one continued, state media reported. 

Three top Xiaoyi city officials were removed from their posts as a result of the mining accident, the local government announced Friday.

Seven suspects have been detained over the accident and police said they were searching for others -- including the mine's owner, reportedly a local villager who fled after the accident.

State TV showed rows of orange-clad rescuers wearing hard hats lifting the miners out on stretchers to ambulances.

China generates about 60 percent of its energy from burning coal, and had ramped up output in recent months to ease an energy shortage that had caused power cuts and forced factories to close.

Authorities said Thursday that high demand for coal has pushed up prices and cases of illegal mining.

The Work Safety Committee of the State Council and the Ministry of Emergency Management called for coal-producing provinces to investigate illegal mines, saying those involved should face criminal proceedings.

Mining accidents are common in China, where the industry has a poor safety record and regulations are not necessarily enforced.

Nineteen miners died after being trapped underground in a single mine collapse in September.

And in January, 11 of a group of 22 miners were dramatically rescued from a collapsed mine in eastern China after they spent two weeks trapped hundreds of metres underground.

China's mine safety body said last week that improved workplace safety meant there had been 336 mine accidents in 2021 so far -- 59 fewer than last year.

But it warned of an increased risk of incidents in December as mines sacrifice production safety for output as the end of the year nears.