Chicago police on Sunday morning were investigating a deadly mass shooting in the city's River North district.

The shooting happened at 2:35 a.m. in the 400 block of North LaSalle Drive, near Hubbard Street.

Police said the victims were getting into a car when four unidentified suspects approached them on foot, pulled out guns, and opened fire.

A 34-year-old man suffered multiple gunshot wounds to his body and was taken to Northwestern Memorial Hospital, where he died.

A 36-year-old man was shot in the chest, a 43-year-old man was shot in the back, and a 35-year-old man suffered multiple gunshot wounds throughout his body. All were taken to Northwestern Memorial Hospital in critical condition.

Police said the armed suspects then got into a car and drove away from the scene. 

For most of the morning, police focused on a green Porsche, which was surrounded by evidence markers. No one was in custody.