A steel structure at a road construction site in Busan collapsed Thursday killing four workers.

Three buried workers were unearthed and taken to hospital but died about an hour after the accident, the police said. The other worker was found dead later.

According to witnesses, the structure buckled during the process of pouring concrete onto the road under construction.

The police suspect that the structure failed due to the weight of the concrete. The authorities plan to question those in charge of the site regarding safety protocols.

The road in question, which is being built by Samjung Construction on a subcontract from SK Engineering and Construction, is designed to link two bridges that cross the bay near Busan Port. 

By Choi He-suk (cheesuk@heraldcorp.com)