Beijing - A cave-in killed at least one person and left 16 missing after trapping dozens on Saturday afternoon in a tunnel under construction for a subway line in the eastern Chinese city of Hangzhou, state media said.

A road caved in above the tunnel, trapping construction workers and causing several vehicles to fall into the hole, the official Xinhua news agency said.

About 2,000 rescue workers rushed to the site and pumped water out of the tunnel", the agency quoted rescue officials as saying.

At least 13 vehicles plunged into a 15-metre-deep crater about 75 metres long and 50 metres wide, it said.

Local hospitals treated at least 19 rescued people, while witnesses and rescuers earlier said at least 50 people were trapped.

The exact number trapped was still unknown, the agency said.

"There is some distance between where I was working and the cave-in site," it quoted Zhu Juzhong, a rescued worker, as saying.

"Lots of workers immediately rushed to the hoist to be lifted above ground," Zhu said.

"Some colleagues who moved slowly were buried," he said.

About 30 workers managed to escape on the hoist, and three fell from the hoist during the rush, Zhu added.

Twenty-seven people travelling on a bus that was trapped in the crater escaped after the driver opened the door, witnesses said.

Water from a river flowing beside the cave-in site soon seeped into the tunnel, the agency said.

Its depth is estimated at about four or five meters and rising, and five frogmen were searching for people trapped in vehicles, it said.

Three vehicles had been pulled out by 8:45 pm, it said.