Cowboy builders used foam to construct the guardrails of a bridge in China.

Shocked locals discovered blocks of Styrofoam beneath the structure's surface in Chengdu, Sichuan, on February 23.

Footage shows one of the guardrails damaged, as the man filming scrapes off foam pellets with his hand.

He said in the video: 'I don't know whether they were cutting corners or trying to save costs.'

The guardrail appeared to have only a concrete coating on the outside, with foam stuffed inside.

Officials said they would investigate the structure, which poses a clear safety hazard.

A staff member from the Jinniu District Agriculture and Water Affairs Bureau told local media that authorities were taking the incident seriously and launching an investigation.

They added: 'We are looking into whether there are energy-saving and environmental protection requirements. We have already contacted the construction firm to retrieve information.'