Three workers were killed and four others injured when a bridge being prepared for demolition partially collapsed Oct. 16 in southern Mississippi.

The bridge carrying State Route 149 over the Strong River in Simpson County, located southeast of Jackson, Miss., had been closed to traffic for about a month as part of a bridge replacement project, Mississippi Dept. of Transportation officials said in a statement. Columbia, Miss.-based contractor T.L. Wallace Construction was working on the bridge ahead of a planned demolition, MDOT added. Simpson County Coroner Terry Tutor identified the three who were killed as Kevin Malone, Charles Igleharte and Charles Badger. All three were employees of T.L. Wallace, the contractor said in a statement.

An MDOT inspector was at the site when the bridge collapsed, but was unharmed, officials added.

The 292-ft-long steel stringer or girder bridge with a cast-in-place concrete deck was built in 1943 and sees an average 2,600 vehicles per day, according to National Bridge Inventory data posted online by the Desert Sun newspaper.

MDOT plans to replace the bridge under a $25-million contract with T.L. Wallace that also includes three other bridge replacements along Route 149. In August, the most recent update shared by officials, bridge decks for the first two bridges had been replaced and crews were doing earthwork to prepare the approaches. The Strong River Bridge is due to be replaced after the others, which are expected to be completed next year. 

The cause of the collapse is unknown and under investigation, MDOT said. The project is now on hold until the investigation in completed.

In a statement, T.L. Wallace President Douglas Blackwell said called the three workers killed in the collapse "cherished members of our community and our team." He added that the company is cooperating with the investigation.

OSHA records show inspectors visited one of the other bridge replacement sites earlier this year for a planned inspection. No citations were issued. OSHA is also investigating the incident, a representative says.

This article was updated Oct. 17 with new information.