A gunman opened fire at a basketball league match in Philadelphia Monday evening, wounding six spectators, authorities said.

The five men and a woman who were wounded, one of them critically, at the Kingsessing Recreation Center in southwest Philadelphia were taken to the Hospital of the University of Pennsylvania, Reuters reported.

We don't know why it happened, we don't have a motive, said Detective Orlando Ortiz, who was investigating the case.

Police said the unidentified suspect fled the scene and that they were interviewing witnesses. No arrest has been made.

The incident happened a little before 9 p.m. during the halftime of an adult league game, CBS News reported. There were about 500 spectators watching the game. The seriously injured male was shot in the stomach.

According to the police, at least 11 shots were fired, and a person in the crowd had returned fire too. Police chased a person who left his gun and ran away but said that weapon had not been fired.