CHICAGO (STMW) – Four people were critically injured early Saturday when a police sergeant shot a driver armed with a knife after a car accident in the Loop.

A driver armed with a knife exited his vehicle after a car accident and attempted to harm the other driver at 1:52 a.m. at LaSalle and Monroe streets, said police News Affairs Officer Ronald Gaines, citing preliminary information.

A security guard from a nearby building was injured while trying to intervene between the two drivers, Gaines said. An on-duty police sergeant arrived on the scene and told the driver to drop the knife. The driver refused and came towards the sergeant, who shot the person.

Two people were taken in critical condition to Northwestern Memorial Hospital, Knight said. Two others were taken in critical condition to John H. Stroger Jr. Hospital of Cook County, according to Fire Media Affairs spokesman Will Knight, who had no immediate details on their injuries.

An EMS Plan 1, which sends five ambulances to the scene, was called for the accident and shooting.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2012. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)