Police raided the offices of the Korea Expressway Corporation and its contractors as part of a probe into a deadly bridge collapse at a construction site in Anseong, Gyeonggi Province, earlier this week. 

The Gyeonggi Nambu Provincial Police sent investigators to seven locations Friday morning, including the headquarters and offices of Hyundai Engineering, which was in charge of the construction project; the Korea Expressway Corporation, which placed the construction order; and two subcontractors.

About 80 people, including labor ministry officials, took part in the raid. 

The police and the labor ministry plan to secure documents and materials related to construction planning and procedures. 

Four workers died and six others were injured after a bridge collapsed at the highway construction site in Anseong on Tuesday morning.