Pedestrians in a southern Chinese city had little warning when a 12-floor building was suddenly demolished.

Video shows the panicked reaction of people in the city of Changzhou when the 34-year-old Zhonglian building was blown up by a demolition crew last Tuesday.

Footage captured screams and the scenes of people fleeing as the 55-metre structure came crashing down beside a busy street in the middle of the afternoon.

Massive clouds of dust are shown spreading from the demolition site into nearby streets.

The building was torn down to make way for a planned rail line, reports local news agency Sina.

A spokesman for Changzhou city authority said officials ensured the building was empty and traffic in the area was halted but video showed many pedestrians apparently unaware of its destruction.

“We hired the most powerful workers in the province to ensure that the last pillar of the building was collapsed,” the spokesman said.