At least 35 people have lost their lives in an attack on a night club in Istanbul, the city’s governor has said.
Among the dead is one police officer, Vasip Sahin stated, adding that it was a terror attack.
At least another 40 were injured in the attack which took place in the Reina nightclub, in the Ortakoy area, at about 01:30 local time (23:30 GMT).
One attacker was involved, the governor said, while CNN Turk reported he was dressed in a Santa Claus costume.
There were reportedly several hundred people in the nightclub at the time, some of whom are believed to have jumped into the Bosphorus to escape.
Istanbul had been on high alert for any terror attacks, with some 17,000 police officers on duty in the city.
This is the latest in a string of attacks in Turkey over recent months, many carried out by so-called Islamic State (IS) or Kurdish rebels.
Russian ambassador Andrei Karlov was shot dead by off-duty Turkish policeman Mevlut Mert Altintas as he gave a speech in the capital Ankara in December.
After the shooting, the killer shouted the murder was in revenge for Russian involvement in Syria.