A subway train derailed in Brooklyn Tuesday night outside a busy station, injuring 89 people.

Officials say 53 people were treated at hospitals and three people were seriously hurt, but none of the injuries were considered life-threatening. One victim had a heart condition, and the other two suffered head injuries.

New York Mayor Rudolph Giuliani told reporters at the scene that people were shook up pretty badly. "Heads were injured as they bounced back and forth." he said.

Hundreds of people were on the subway train, which was headed for Manhattan, when three cars jumped the tracks just before 10 p.m. The wheels of the third car skipped, causing it to derail.

Twenty metres of track was damaged. Repair crews worked through the night replacing the track. Subway service resumed early Wednesday morning.

Giuliani said the cause of the accident was under investigation.