Emergency rescuers in northern China were undertaking a major operation on Sunday to find two people still missing after a gas explosion at a coal mine killed at least 82.

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, according to state media.

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

AFP journalists saw police blocking the road leading to the mine late Saturday, allowing only authorised vehicles to enter.

Helmeted rescuers took turns descending into the shaft overnight to look for the two missing workers, state media reported.

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

Chinese authorities launched an investigation into the blast, the worst since 2009 when 108 people were killed in a mine explosion in northeastern Heilongjiang province.

Preliminary findings showed the company operating the mine had committed "serious illegal violations", authorities told a press conference broadcast by the state-run CCTV.

"Those found responsible will be severely punished in accordance with laws and regulations," they added.

A person "responsible for" the company involved had been "placed under control in accordance with the law", Xinhua said.

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.

- Sulphur smell -

Wounded survivor Wang Yong told CCTV he heard no sound 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.

"When I smelled it, it was the smell of sulphur like when people set off firecrackers. When the smoke came down, I shouted for people to run," he said.

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.

Shanxi, one of China's poorer provinces, is the centre of the country's coal-mining industry.

Mine safety in China has improved in recent decades, but accidents still occur in an industry where safety protocols are often lax and regulations vague.

In 2023, a collapse at an open-pit coal mine in the northern Inner Mongolia region killed 53 people.

China is the world's top consumer of coal and the largest greenhouse gas emitter, despite installing renewable energy capacity at record speed.