One person is in custody after a man was killed during a fight between five or six people at Front Street East and Market Street, Toronto police say.

The victim, a 50 year-old man, suffered a "significant head injury" during the altercation and was rushed to hospital without vital signs, where he was pronounced dead.

The 43-year-old man in custody has not yet been charged.

Toronto police Insp. Steve Molyneaux says the homicide unit is investigating.

"I can tell you that we did receive a radio call around 9:30. At this point, it's too early to discuss exactly what happened. It is still under investigation. We have several people we need to speak to."

Insp. Steve Molyneaux says police are questioning several people in relation to the altercation. (CBC)

Another man was taken to hospital with unknown injuries.

They don't know yet if any weapons were involved.

Forensic teams are on scene in the pedestrian walkway around the Rainbow Cinemas Market Square where the fight occurred.

Police have surveillance footage from the area and they are also speaking with several witnesses.

Anyone with information is asked to call 51 Division at (416) 808-5100.