CHICAGO (CBS) — Chaos erupted at a block party in the Back of the Yards neighborhood overnight, when an argument escalated into deadly gunfire, and a witness died after suffering an asthma attack.

Chicago police were searching for the shooter who opened fire from a vehicle in the 800 block of West 50th Place around 12:15 a.m., striking four people.

A 33-year-old woman and a 25-year-old man both were shot in the neck. The man was pronounced dead at Stroger Hospital. The woman was pronounced dead at St. Bernard Hospital.

Two other women, ages 21 and 25, were wounded in the attack. The younger woman was being treated at St. Bernard Hospital for a gunshot wound to the hand, while the older woman was taken to Stroger Hospital with gunshot wounds to the back. Both of their conditions had stabilized, police said.

Police said a 16-year-old girl who witnessed the shooting suffered an asthma attack, and was taken to St. Bernard Hospital, where she was pronounced dead about 90 minutes later.

Witnesses said people were gathered for a birthday block party, when someone at the party got into an argument with someone in a vehicle.

The person in the vehicle pulled out a gun and opened fire. Witnesses said the fight started as a dispute over a parking space.

The victims’ identities have not been released.

No one was in custody Thursday morning. Area Central detectives were investigating.