A massive sinkhole reportedly is still expanding after swallowing a complex of several buildings in Guangzhou, China, on Monday.

The 30-foot-deep (9 meters) sinkhole is spread over about 3,200 square feet (300 square meters), according to the blog Shanghaiist.

The sinkhole developed in an area where construction workers had been digging for a subway line. The workers noticed that the ground was sinking rapidly and were able to evacuate some 300 people from the buildings before the structures turned to rubble, according to the Sydney Morning Herald.

Gas, water and electrical lines were severed in the collapse, resulting in an area-wide blackout.

This isn't the first time the neighborhood has dealt with sinkholes: In 2004, according to Shanghaiist, a 320-square-foot (30 square meters) sinkhole opened up; the cause was reportedly the construction of another subway tunnel.

Some sinkholes form naturally in areas with salt beds or easily dissolved bedrock such as limestone, according to the U.S. Geological Survey. When groundwater flows through these rocks, it eats away at them, leaving behind underground holes and caverns. When the roof collapses over one of these caverns, it brings the land above down with it.

Other sinkholes can be caused by human activity, either underground construction or the diversion of subterranean water for drinking or agriculture. The lack of water weakens the underground structure, and the land sinks — sometimes gradually, sometimes in a catastrophic collapse.

A growing number of construction-related disasters in China have been blamed on lax safety standards throughout the fast-growing nation as the government speeds up development projects, the Morning Herald reports.

In August, a freeway in northeast China collapsed less than a year after completion, according to the Morning Herald. It was the sixth major bridge collapse since 2011. One month later, 19 people were killed in central Hubei province when an elevator plunged 30 floors and crashed at a building site.

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