Four people were wounded in a shooting between the occupant of a car and a man standing on an East Oakland sidewalk Saturday morning, police said.

The four — three men and one woman — were being treated for what police Officer Kevin McDonald described as non-life-threatening injuries.

Police said a car was driving by when a 37-year-old man shot at it, and someone in the car fired back. Those injured were the gunman, two other men on the sidewalk and an 18-year-old woman who was a passenger in the car.

The woman was driven to a hospital by a 17-year-old boy, who was detained for questioning by police, The Oakland Tribune reported.

A motive for the shooting hasn't been established, and no additional details were released.

The shooting happened about two hours before a gun buyback program, intended to get firearms off the street, was to begin less than a mile away. The Tribune reported the turnout was high, with a line of cars stretching for blocks before the event began.

Capt. Ersie Joyner III said more than 250 firearms had been turned in by the time the buyback ended, and drivers who were still in line had to make arrangements to redeem their guns at a later date.

The buyback program offers $200 each for up to three weapons per person. Only gun owners with verified residence in Oakland or San Francisco qualify.