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.

One man, smoking nervously on a curb, told AFP that calls to his brother -- a father of three -- "wouldn't go through" since the blast.

He said he had "no idea how the accident actually happened" and that their parents were still unaware their older son was missing.

"I don't dare tell them," he said, asking not to be named.

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 news 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.

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

- 'It would have been us' -

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

Miners working at the Liushenyu shaft accused their employer of a lack of care, telling AFP they had to buy their safety helmets with their own money.

"From what I've seen, the management (at this company) is the worst," said 58-year-old miner from Shandong, who has worked in several coal mines over the last three decades.

Wishing to remain anonymous for fear of repercussions, miners told AFP they had been working a morning shift on Friday and were not in the mine during the gas explosion.

"If we had been (working) a few hours later, it would have been us," the 58-year-old said.

AFP has contacted Tongzhou Group for comment.

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.

- Rescue efforts -

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.

They have been taking turns descending into the shaft to look for the two missing workers, sending down a robot to probe the mine conditions, state media reported.

"The main task is to conduct a thorough, carpet-style search of the entire tunnel, covering every possible location," one of the rescuers told CCTV.

"The slope is steep here. Some areas are quite narrow, so moving around takes a relatively long time, especially now with large equipment."

The blast is the worst since 2009 when 108 people were killed in a mine explosion in northeastern Heilongjiang province.

Injured survivor Wang Yong told CCTV: "I didn't hear any sound at all, but then a cloud of smoke appeared".

"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".

Taiwan's President Lai Ching-te said the self-ruled island -- claimed by Beijing -- "stands ready to provide humanitarian assistance".

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.