At least one person was killed and 16 injured after an explosion at a chemical park in the western German city of Leverkusen on Tuesday, the site's operator said. Four other people are still missing.

The blast happened at around 9:40 a.m. (0740 GMT) "for still unknown reasons," Chempark operator Currenta said in a statement, adding that a fire that had broken out had been extinguished.

Witnesses saw a column of smoke rising above a Bayer chemical plant inside the park, reported Reuters.

Police have cordoned off the plant's surrounding areas, and a fire brigade has informed the residents nearby to close their doors and windows.