ISTANBUL - Two buildings collapsed in central Istanbul on Friday, sending a haze of dust through one of the city's busy tourist districts, but officials said no one was believed to have been injured . The immediate cause of the collapse was unknown. The buildings , at least one of which was five storeys tall, were in a street off of Istiklal Avenue, in a district of old buildings and shops popular with tourists and locals. No one was believed to have been killed or injured , Istanbul Governor Vasip Sahin told CNN Turk.