At least nine people were killed and eight seriously injured in South Korea when a five-storey building – which was in the process of being demolished – collapsed suddenly onto a bus, officials at a local fire station said.

The accident happened on Wednesday afternoon when the bus was stopped on the street next to the demolition site in Gwangju, some 270km (168 miles) southwest of the capital, Seoul, officials at the Gwangju Fire and Safety Headquarters said.

Dramatic television footage showed the bus, which had 17 people on board, being buried in debris and smothered by a huge cloud of dust as the structure gave way.

Yang Ik-je, who runs a shop across the road from the construction site, said he ran outside, jolted by the loud noise that made him feel as if “the earth was shaking”.

“I could not see the road clearly, as if it were shrouded in thick fog,” he told Yonhap news agency. “I checked the CCTV to find out that the building collapsed onto a bus.”

The reason for the collapse was unclear, and a police investigation is under way, officials said.

All the workers on the demolition site had been evacuated before the collapse.

South Korea has been taking steps to improve its infrastructure safety record following a number of disasters.

A department store collapse killed more than 500 people in 1995, the country’s worst peacetime disaster. A bridge collapse the year before killed 49 people.