MIANYANG, SICHUAN - Two workers in China's Sichuan province were rescued by passers-by after a four-storey tall scaffolding collapsed while they were were on it.

The accident happened on Wednesday (Dec 7) afternoon in Mianyang city in south-west China, state broadcaster CCTV said.

Video footage showed the scaffolding detach from a building, said to be a cinema, and gradually crash to the ground.

Two workers who were on it were trapped underneath. A passer-by also injured his knee while trying to avoid the collapsing structure.

At least 20 people joined in the rescue effort, CCTV said. They also called rescue services.

One worker was seriously injured, but both are now in a stable condition, a Sichuan paper said.

The two workers were changing advertising displays on the building facade, according to the report.