At least 14 people have been killed in a shooting at a Batman film premiere in the US city of Denver, police say.

About 50 people have been injured in the incident at the cinema complex in the suburb of Aurora, BBC reports.

Witnesses say a gunman wearing a gas mask opened fire during a midnight showing of The Dark Knight Rises.

A man was arrested in a car park nearby in possession of a rifle and hand-gun. He told police that explosives were stored at his home.

Police chief Dan Oates told reporters that an apartment block in the north of Aurora had been evacuated as a consequence of that information.

More weapons may have been left in the cinema, he said.

Ten people were killed at the cinema and four others died later at hospital of their wounds, the police chief said.

There are reports that the gunman also released a smoke bomb during the incident. Many ambulances are at the scene.

A witness told 9News that during a shooting scene in the film he heard loud bangs and a lot of smoke and initially thought they were live special effects put on by the cinema.

Projectiles came through the wall from the neighbouring theatre screening, the witness said.

CNN quoted one witness saying: "A guy slowly making his way up the stairs and firing - picking random people."