Footage aired on local television showed the site of the accident after the tram rammed into the side of the bus.
Emergency services personnel were seen attending to injured people in the Eyupsultan district.
At least four people were seriously injured in the accident, according to the district governor, Ihsan Kara.
The bus-tram line between the T5 Cibali-Alibeykoy and Cibali-University stations was temporarily suspended.
The accident occurred due to a signaling failure on the tram line, local media claimed. “It was obvious that this would happen. There were problems with these lights for about 10 days and it was repaired many times. The green lights have been on for both cars and the tram,” said a witness of the accident.