QINYUAN (AFP)

Rescuers in northern China searched on Sunday for two people still missing after a gas explosion killed 82 in a mine that authorities said was beset by serious safety violations.

The blast at the Liushenyu shaft in Shanxi province on Friday was the country's worst mining disaster in nearly two decades, with 247 workers underground at the time, authorities said.

AFP journalists saw relatives anxiously waiting by a checkpoint blocking the road leading to the mine on Sunday, hoping for news of their loved ones.

Authorities launched an investigation into the blast, saying preliminary findings showed the Tongzhou Group operating the mine had committed "serious illegal violations". 

"Those found responsible will be severely punished in accordance with laws and regulations," officials told a new conference broadcast on state-run CCTV.

More than half of the workers in the shaft on Friday had gone down without being properly registered, state media said, citing a personnel board at the site.

The miners are normally required to undergo facial recognition checks or take location-tracking cards before their descent.

A person "responsible for" the company had been "placed under control in accordance with the law", Xinhua news agency reported earlier.

Hundreds of rescuers rushed to the site after the explosion, with medical teams taking 128 people to hospital as of Saturday evening, loaded into ambulances and carried on stretchers.

Helmeted rescuers took turns descending into the shaft overnight to look for the two missing workers, sending down a robot to probe the mine conditions, state media reported.

"As long as there is hope, we will make every possible effort," one rescuer told Xinhua.

The blast in Shanxi, the centre of China's coal-mining industry, is the worst since 2009 when 108 people were killed in a mine explosion in northeastern Heilongjiang province.

The State Council, China's cabinet, ordered nationwide "tough crackdowns on illegal and unlawful activities", including the falsification of safety data, unclear headcounts of underground workers, and illegal contracting.

Injured survivor Wang Yong told CCTV he heard nothing but smelled sulphur when the explosion happened.

"I didn't hear any sound at all, but then a cloud of smoke appeared," the miner said. "It (had) the smell of sulphur like when people set off firecrackers. When the smoke came down, I shouted for people to run."

He recalled seeing people choked by the smoke before he fainted.

"After more than an hour, I came to on my own, and then I woke up the person next to me" and got out, he told CCTV.

Foreign leaders extended condolences to the victims and their families, with Japanese Prime Minister Sanae Takaichi saying she was "praying for the rescue of as many people as possible".

India's Narendra Modi expressed hope that "the bereaved families find strength in this tragic hour".