ISTANBUL (CBSNewYork/CBS News/AP) — An armed assailant believed to have been dressed as Santa Claus opened fire at a nightclub in Istanbul during New Year’s celebrations, killing at least 35 people and wounding 40, Istanbul’s governor said.

Gov. Vasip Sahin said the attacker, armed with a long-barreled weapon, killed a policeman and a civilian outside the club before entering and firing on people partying inside. He did not say who may have carried out what he called a “terror attack.”

As CBS2’s Jessica Moore reported, dozens of the injured were rushed to hospitals Sunday morning local time.

“Forty people are receiving treatment in hospitals,” Sahin said.

“Unfortunately (he) rained bullets in a very cruel and merciless way on innocent people who were there to celebrate New Year’s and have fun,” Sahin told reporters.

PHOTOS: Dozens Dead In Istanbul Nightclub Shooting

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Media reports said the assailant entered the Reina nightclub, in Istanbul’s Ortakoy district, at 1:45 am, dressed in a Santa Claus costume.

Some customers jumped into the waters of the Bosporus Strait to escape the attack, the report said.

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

Police in riot gear and machine guns backed up by armored vehicle blocked the area close to the Reina night club, one of the most popular night spots in Istanbul in the amid heavy rain. Several ambulances flashing blue lights arrived on the scene, some taking wounded to Istanbul hospitals.

The attack occurred shortly after midnight in the club where an estimated 600 people celebrated New Year’s eve. Several shocked revelers were seen fleeing the scene after the attack and the music fell silent.

Eyewitness Sinem Uyanik told the Associated Press she saw several bodies inside the Istanbul nightclub that was attacked during New Year’s celebrations.

Her husband Lutfu Uyanik was wounded in the attack.

“Before I could understand what was happening, my husband fell on top me,” she said outside Istanbul’s Sisli Hospital. “I had to lift several bodies from on top of me before I could get out.”

Her husband was not in serious condition despite his wounds.

The club is located close to recent suicide attacks that killed dozens near a soccer stadium.

Early Sunday morning, police cordoned off a large section of the city of 14 million people. At least 17,000 officers were deployed.

Istanbul had already been under heavy security surveillance during the festivities, with police mounting machine guns and armored vehicles parked on the streets.

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.

White House spokesman Eric Schultz says President Barack Obama was briefed on the attack by his national security team and asked to be updated as the situation develops. Obama is vacationing in Hawaii this week with his family.

White House National Security Council spokesman Ned Price says the attack on “innocent revelers” celebrating New Year’s shows the attackers’ savagery. He says the U.S. sends thoughts and prayers to the relatives of those killed.

Price said the U.S. supports its NATO ally Turkey as both countries fight terrorism.

The NYPD Counterterrorism Bureau said via Twitter that with regard to the Istanbul shooting, there were no specific threats to New York City. But the bureau said it is closely following developments.

The U.S. State Department also advised Americans to avoid the area.

“The U.S. Consulate General in Istanbul reminds U.S. citizens that extremist groups are continuing aggressive efforts to conduct attacks in areas where U.S. citizens and expatriates are present,” the State Department said.

Meanwhile, Gov. Andrew Cuomo issued a statement saying the people of New York state stand with Istanbul.

Cuomo said he has directed all New York state law enforcement to be vigilant during New Year’s Eve celebrations around the state. He said the New York State Police, the New York State Emergency Operations Center, the New York State Intelligence Center and the Division of Homeland Security and Emergency Services are watching for developments and any potential threats.

New Yorkers statewide were advised to report any suspicious activity Counter Terrorism Center at the New York State Intelligence Center Terrorism Tip Line, at (866) SAFENYS (1-866-723-3697).

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