A powerful blast occurred next to a tram stop in Istanbul’s historic downtown district. A group of German tourists is reported to have been in the area at the time the explosion went off, reports Associated Press.

Police cars and fire trucks arrived in large numbers on the scene of the blast. Bomb disposal experts are currently trying to establish what kind of explosive device was used.

The exact number of those injured in the blast is not yet known but Turkish TV Channel ТРТ puts death toll at 1 or three, while British Sky News TV Channel reports two people killed, claiming that one of them was a suicide bomber. According to an unconfirmed report released by Euronews, ‘at least 10 people were killed in the blast’.