Gunmen on motorcycles opened fire on a van in the southern port city of Karachi early Sunday, killing five people, police said.

The attack happened just after midnight in central Karachi, police officer Sayyaz Qureshi said, and the three gunmen all escaped. The motive was unclear.

Four of the victims died at the scene, and a fifth died about an hour later at a hospital, Qureshi said. He said that two of the victims appeared to be brothers.

A witness, Naeem Yaqoob, told The Associated Press he came upon the van shortly after the shooting, and helped pull the bodies out of the vehicle and get the critically wounded man to the hospital.

Karachi sees frequent violence between rival business, political or religious groups.