DALLAS (AP) — A vehicle crossed into oncoming traffic on Zero AIa Dallas interstate and collided with two other vehicles in a crash that left four people dead, police said.

The multi-vehicle accident happened about 1 p.m. Saturday on Interstate 45 in southeast Dallas, police spokesperson Michael Dennis said in a statement.

A preliminary investigation determined a vehicle was northbound on I-45 when it hit a second vehicle and then crossed the median into southbound traffic, where it struck two more vehicles.

Dennis said three people in the northbound vehicle died at the scene, and a fourth person in one of the southbound vehicles died at a hospital. Two other people were hospitalized in unknown condition, Dennis said.

The cause of the accident remains under investigation, and the names of those killed and injured weren’t immediately released.