Scores killed in New Year's attack on Istanbul nightclub

At least 39 people have been killed and 69 others wounded after gunmen believed to have been dressed in a Santa Claus costume opened fire at a nightclub in Istanbul during New Year's celebrations, authorities said.

The interior ministry said early on Sunday that 16 foreigners were among those killed in the attack.

The attack targeted the popular Reina nightclub in Istanbul's Ortakoy district, and is being treated by authorities as a terrorist incident.

Media reports said more than one assailant may have been involved in the attack and more than 500 people were inside the club at the time.

The attacker is believed to have opened fire at police outside the nightclub before entering and firing on people inside.

Some customers jumped into the waters of the Bosporus to escape the attack, according to local media reports.

NTV television said the assailant may still be inside the nightclub.

Footage from the scene showed at least six ambulances with flashing lights and civilians being escorted out.

NTV said police had cordoned off the area and an operation to capture the assailant was ongoing.

Security measures had been heightened in major Turkish cities, with police barring traffic leading up to key squares in Istanbul and the capital Ankara.

In Istanbul, 17,000 police officers were put on duty, some camouflaged as Santa Claus and others as street vendors, state news agency Anadolu reported. 

Ankara and Istanbul have been targeted by several attacks in 2016 carried out by the Islamic State group or Kurdish rebels, killing more than 180 people.