Fire broke out on the roof of Chicago's vacant former post office Tuesday where a movie crew had been filming scenes for the upcoming "The Dark Knight" reports The Associated Press.

Fire department spokesman Kevin MacGregor said a building engineer suggested the fire might have started in the ventilation system. Whilst there was no injuries, it was unclear if the fire was related to the filming.

Crews had been filming there all week so office worker Pete Kearney says of the smoke seen on Tuesday morning - "We assumed it was part of the movie."