Construction workers, cars and a bus disappeared into a huge crater created by the collapse of a half-built subway tunnel in the eastern Chinese city of Hangzhou.
All 27 people on the bus scrambled to safety but at least three people died - one a worker, another a passenger in a taxi.
Rescue teams called in scuba divers as water from a nearby river rushed into the crater that measures 15 metres deep and 75 metres across.
At least 17 people are missing - most construction workers who were building a 70-kilometre extension to the city's subway system.
Nineteen people are being treated in hospital, some for fractures.
About 2000 emergency workers are struggling to pump out the water.
They expect to retrieve more bodies.
Workers released from hospital tell of colleagues who moved too slowly vanishing under a tide of mud.
China's construction industry has been plagued by corruption, poor standards and shoddy materials as the country's booming economy fuels a rush to expand infrastructure.