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.

Cook County Crime Stoppers announced Sunday that it is offering a $10,000 reward for information leading to an arrest in the ass shooting.

"This was a brazen and violent act that took one life and left three others fighting for their lives," Paul Rutherford, executive director of Cook County Crime Stoppers, said in a news release. "Someone knows who is responsible. Your information, no matter how small it may seem, could be the key to bringing justice to the victims and their families. We want the public to know that you can provide information anonymously and be eligible for a significant cash reward by calling 1-800-535-STOP or going online at www.CPDTIP.com."