At least three people were killed and 17 more were trapped when a half-built subway tunnel in the eastern Chinese city of Hangzhou collapsed, leaving a huge crater that also engulfed 11 vehicles, state media said on Sunday.
Workers building the new metro system scrambled to escape the slow cave-in on Saturday, which left a pile of jumbled steel poles jutting out of a gaping giant crater and forced the evacuation of nearby homes, Reuters reported.
"Lots of workers immediately rushed to the hoist to be lifted above ground," said Zhu Juzhong, a 56-year-old worker from southwestern Sichuan province who said about 30 of his colleagues made it onto the lift, but three fell back down during the rush.
"Some colleagues who moved slowly were buried," the official Xinhua news agency quoted him as saying.
Another worker described a desperate climb up a steel cable after missing the lift because he was too far away.
The cave-in began mid-afternoon and left a hole 15 meters deep and 75 meters long, Xinhua said. Vehicles including several taxis and a public bus fell into the chasm.
State media initially said more than 50 were feared trapped, but after nearly 30 people on board the bus were helped to safety only 17 people were registered as missing.
Rescue efforts were complicated by a nearby river which started to seep into the devastated tunnel.
"There is a slim chance for the survival of trapped workers, because of heavy flooding in the crater," spokesman Wang Guangrong told Xinhua. By Sunday morning waters had receded to around three meters from a high of six metres, he added.
The construction company has sent workers to reinforce remaining parts of the tunnel, but the government did not rule out the possibility of further collapses, Xinhua said.
The accident was not the first time China's efforts to upgrade its public transport networks have met with tragedy.
In March last year a Beijing subway tunnel being built for the 2008 Olympics collapsed, burying six workers.
In Shanghai, where a subway tunnel collapsed in 2004, the mayor warned this summer that the city's frenzy of construction to extend the network had reached an "extreme level," making safety a worry.
Hangzhou launched work on its subway system in March last year, building three lines designed to cover nearly 70 km (44 miles) by 2011, at a total cost of 35 billion yuan ($5.13 billion).