A 29-year-old man was shot while he was on his way to work on Chicago's State Street Bridge over the Chicago River Monday evening.

The incident occurred at the peak of rush hour at 5 p.m. and shocked onlookers.

The 29-year-old man was walking north on the west side of the bridge, near Wacker Drive, when the gunman approached and shot him in the head at very close range about 5 p.m., Belmont Area Commander Gary Yamashiroya said, according to the Chicago Tribune.

"I heard a boom, like a gun sound. All you can see is the man fall and the other man took off, over there," a witness, Samleiso Lewis, told CNN affiliate WLS.

The victim was rushed to the Northwestern Memorial Hospital in critical condition. He was able to speak to the police from the hospital. However they have no further information on his condition.

The unidentified suspect reportedly fled after shooting the man, said the police.

Police believe that the shooting was not unplanned. They do not have anybody in custody as yet.

The gunman was last seen running away from the scene carrying a handgun, witnesses told the police who are reviewing footage from the many surveillance cameras in the area.

The Chicago Tribune reported about the witnesses informing the police of the gunman fleeing south on State and possibly heading towards the Millennium Park Metra station.