Islamic State has now claimed responsibility for the massacre at the Reina club, in which 69 people were wounded, four critically.
Police are said to be investigating whether it was the same terror cell that carried out the deadly suicide bomb and gun attack at Istanbul’s Ataturk airport last June.
There are also reports Turkey received an intelligence tip-off from the US about the threat of a New Year attack although it did not give details of where it could take place.
Twenty-five of the dead were reportedly foreign citizens, including an 18-year-old Israeli woman, three Indians, three Lebanese, a woman with dual French-Tunisian citizenship and her Tunisian husband, three Jordanians, a Belgian national, a Kuwaiti citizen and a Canadian.
CCTV footage has emerged of the moment the killer opened fire outside the club before storming the building that was packed with up to 600 revellers celebrating the New Year.
He first fatally shot policeman Burak Yildiz and travel agent Ayhan Arik at the front of the venue around 1.15am local time, before randomly attacking people inside the nightspot.
It was initially reported the assailant, armed with a long-barrelled gun, had been wearing a Father Christmas outfit but this was later denied by the Turkish prime minister.
The attacker is believed to have changed his clothes to escape the scene.
“The search for the terrorist continues… I hope (the assailant) will be captured quickly, God willing,” said interior minister Suleyman Soylu.
He added: “This was a massacre, a truly inhuman savagery.”
Witnesses described diving under tables as the assailant opened fire, while one reveller told how she had to lift dead bodies off her to escape the building after the attack.
Some party-goers jumped into the nearby Bosphorus to escape the slaughter in the Ortakoy district.
President Recep Tayyip Erdogan has said the attack was designed to destabilise the country.
The Foreign and Commonwealth Office (FCO) said UK tourists should follow the advice of local authorities while remaining vigilant.
Attempts are being made to see whether any Britons were among the dead and injured.
Prime Minister Theresa May has written to Mr Erdogan to underline the UK’s commitment to defeating terrorism following the New Year attack.
Foreign Secretary Boris Johnson has called the atrocity “cowardly”, while the White House condemned its “savagery”.
The attack happened despite heightened security in major Turkish cities over New Year.
In Istanbul, 17,000 police officers were on duty, some disguised as Santa Claus and others as street vendors, according to state-run media.
Both Ankara and Istanbul were targeted by a series of attacks in 2016 carried out by the Islamic State group or Kurdish rebels and leaving 180 people dead.
Source: Sky News