SHENZHEN, China (Reuters) - At least 85 people were missing in China on Monday a day after a giant flow of mud and construction waste spewed out of an overfull dump in a boomtown and buried 33 buildings in its latest industrial disaster.

The site should have been closed in February, but workers said mud and waste had continued to be dumped there, a news portal run by authorities in the southern city of Shenzhen said.

Premier Li Keqiang ordered an investigation into Sunday’s landslide in the city, just across the border from Hong Kong.

The mudslide smashed into multi-storey buildings at the Hengtaiyu industrial park in the Guangming New District, toppling them within seconds.

The mudslide, covering an area of more than 380,000 square metres (94 acres), was 10 metres (33 feet) deep in parts, Shenzhen Vice Mayor Liu Qingsheng told reporters, according to state news agency Xinhua.

“The mud had been building up for a few years,” said Han Bin, who lives by the site and witnessed the wall of mud sweep towards the buildings. “We didn’t realise this could happen.”

The frequency of industrial accidents has raised questions about safety standards after three decades of breakneck growth in the world’s second-largest economy. Just four months ago, more than 160 people were killed in big chemical blasts in the northern port city of Tianjin.

State television showed the devastation in Shenzhen, with bits of broken buildings sticking up from heaps of mud stretching out over the industrial park.

A sports hall was converted into an emergency shelter where rescue workers gave out food, water and batteries to charge phones.

“The wall of mud came down and hit us within minutes, it was so fast,” said Jiang Xuemin, 44, who lived and worked in the industrial park. “There was so much mud, I just ran,” she told Reuters at the rescue centre.

More than a year ago, a government-run newspaper warned that Shenzhen would run out of space to dump waste from a building frenzy.

Besides new buildings, a network of subway lines is being built, and large volumes of earth are being excavated and dumped at waste sites.

“Shenzhen has 12 waste sites and they can only hold out until next year,” the official Shenzhen Evening Post, published by the city government, said in October last year.

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SNIFFER DOGS

Once a sleepy fishing village on the Communist side of a Cold War frontier, Shenzhen was chosen by Beijing three decades ago to help pioneer economic reforms, and it has boomed ever since.

Almost 3,000 rescuers were at the scene, Xinhua said, with sniffer dogs and drones. Rescuers were focussing on several areas where sensors had detected signs of life, it added.

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The Ministry of Land Resources said the accumulation of a large amount of waste meant that mud was too steep, “causing instability and collapse, resulting in the collapse of buildings”.

Media said no foreign companies were believed to have been affected.

A nearby section of China’s major West-East natural gas pipeline 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 400-metre-long ruptured pipe “has been emptied” and a temporary pipe will be built.

PetroChina wrote on its microblog the pipeline blast had hit at least one industrial user, a Hong Kong power plant operated by Castle Peak Power Co Ltd, a company majority owned by a subsidiary of CLP Holdings, that had switched to coal for power generation.

Fourteen factories, 13 low-rise buildings and three dormitories were among the buildings flattened.

Xinhua said the government revised the number of missing to 85 from 91. Xinhua said 14 people had been rescued and more than 900 people had been evacuated from the site by Sunday evening.