At least 85 people were missing after a huge mound of mud and construction waste collapsed at a business park in southern China and buried 33 buildings in the country's latest industrial disaster.

Premier Li Keqiang ordered an official investigation into Sunday's landslide in the southern boomtown of Shenzhen, just across the border from Hong Kong, which happened four months after huge chemical blasts at the northern port of Tianjin killed more than 160 people.

The mud and waste smashed into multi-storey buildings at the Hengtaiyu industrial park in the city's northwestern Guangming New District, toppling them in collisions that sent rivers of earth skyward.

"The area affected equals 14 soccer pitches - so that gives you an idea of how big this thing was," Al Jazeera's Adrian Brown reported. 

"Most of [the missing] are migrant workers," he said, adding that it is usually migrant workers who are most badly affected by such disasters in China.   

Speaking to the official Xinhua news agency, a local worker said: "I saw red earth and mud running towards the company building." 

I saw red earth and mud running towards the company building. It's been hours after he was buried, and we are quite worried.

Witness

One woman told the Shenzhen Evening News newspaper on Sunday that she saw her father buried by earth in his truck.


READ MORE: Tianjin residents accuse government of negligence


"It's been hours since he was buried, and we are quite worried," she said.

Xinhua said 14 people had been rescued and more than 900 people had been evacuated from the site by Sunday evening.

Rescue operations were slowed by numerous obstacles, including continued rain, low visibility overnight, and mud, Ao Zhuoqian, a member of the Shenzhen fire brigade involved in on-site rescue, told Xinhua.

State television showed scenes of devastation, with crumpled buildings sticking up from heaps of brown mud which stretched out across the edge of the industrial park. The mud had covered an area of more than 60,000 square metres (72,000 sq yards) and was six metres deep in parts, state media said.

Frequent accidents

More than 2,000 rescuers - with sniffer dogs and drones - were sifting through rubble looking for survivors after the landslide left everything covered in mud, leaving only a surface of yellow sand visible, Xinhua said.

The accumulation of a large amount of construction waste meant that mud was stacked too steep, "causing instability and collapse, resulting in the collapse of buildings", the ministry of land resources said in a statement, referencing an investigation from provincial authorities. 

A nearby section of China's major West-East natural gas pipeline also exploded, state television said, though it was not clear if this had any impact on the landslide.

Xinhua said the pipeline was owned by PetroChina, China's top oil and gas producer, that the 400m-long ruptured pipe "has been emptied" and a temporary pipe will be built.

Contacted by Reuters news agency, the company said it was looking into what had happened.

Chinese President Xi Jinping ordered provincial authorities to do everything possible to minimise casualties, treat the injured and comfort family members, Xinhua said. 

The frequency of industrial accidents in China has raised questions about safety standards after three decades of breakneck economic growth.

In one of China's worst landslides in living memory, more than 1,500 people died in 2010 when a barrage of mud slid down a mountainside into a town in the northwestern province of Gansu following torrential rain.

Industrial accidents in China, a familiar theme

Adrian Brown, Al Jazeera's correspondent in China:

Another month, another industrial accident in China. And like recent incidents, this one was also preventable.

Given the scale of the spill, it could have been so much worse. Somehow officials got warning of a massive landslide and managed to evacuate 900 people. Their quick response certainly saved lives. And, as always at times like this, there is no shortage of manpower and equipment.

But in the aftermath of this landslide, which has left 200,000 metres of an industrial area submerged by mud, one obvious question arises.

Why did the authorities allow a man-made mountain of construction waste and soil to be sited so close to a busy factory zone.

The huge tip was in a disused quarry above the zone. Local residents said on social media that they had expressed their concerns about the dump to local officials many times in recent months.

Local media reports say the tip was more than 100m high and appears to have been operated by a private company which was awarded the contract by the local government. So all was apparently legal.

"There are two aspects of this tragedy that are sadly all too common in China," says Geoffrey Crothall of the China Labour Bulletin, a Hong Kong-based NGO that chronicles worker grievances in China.

He told Al Jazeera that "the storage of hazardous waste adjacent to work sites and residential areas was the case in the Tianjin disaster of August 12 this year which killed 173 people".

Many of the missing are thought to be migrant workers, among the poorest people in China. As one of China's key commercial centres, Shenzhen, which borders Hong Kong, is a magnet for millions of them. The destroyed buildings include two worker dormitories. Some simply compacted, testament, says Crothall, to the poor materials used in their construction.

"Many factory buildings are worker dormitories built from cheap, poor-quality materials and are particularly vulnerable to so-called natural disasters."

So a familiar theme of lax safety laws, shoddy construction and possible corruption are emerging once again.

Source: Al Jazeera and agencies