Police in Istanbul are hunting for a gunman who opened fire at a well-known nightclub, killing at least 39 people.
The attack happened at Reina nightclub early on Sunday, as hundreds of revellers marked the new year.
Officials say some 15 foreigners were killed, including citizens from Israel, France, Tunisia, Lebanon, India, Belgium, Jordan and Saudi Arabia.
The attacker left his gun before "taking advantage of the chaos" and fleeing the scene, Turkey's PM said.
Binali Yildirim also confirmed the gunman was not dressed as Santa Claus, contradicting earlier reports.
The attack unfolded some 75 minutes into the new year as around 700 people gathered in the waterside Reina club, one of Istanbul's most upmarket venues.
The attacker shot dead a policeman and a security guard at the entrance before heading into the club, which is popular with celebrities and foreigners.
Eyewitnesses described seeing dozens of bodies lying on the floor. Some revellers reportedly threw themselves into the Bosphorus to escape the carnage.
"Gunshots rang out. When those sounds were heard, many girls fainted," professional footballer Sefa Boydas told AFP news agency.
He said people appeared to be crushed as they ran away. "They say 35 to 40 died but it's probably more because when I was walking, people were walking on top of people."
At least 69 people are being treated in hospital, officials said, with three in a serious condition.
Earlier, Interior Minister Suleyman Soylu confirmed a "manhunt for the terrorist is under way. Police have launched operations. We hope the attacker will be captured soon."
Details of those who died are starting to emerge.
The security guard at the entrance to the club has been identified as Fatih Cakmak.
His brother said he narrowly escaped a double bombing three weeks ago, having been on duty when Kurdish militants launched an attack near a football stadium, killing at least 44 people, mostly police.
Here is what we know of the other deaths:
- Israel has confirmed Leanne Nasser, 19, was killed while out celebrating with three friends
- Three Jordanians are among the dead, Jordan's foreign ministry says
- Lebanon's foreign ministry says three of its nationals have died and another four are injured
- Tunisia's foreign ministry said on Facebook that two Tunisians died. It is not clear if one of those includes the French-Tunisian dual national
- Belgium's foreign ministry confirms a Belgian-Turkish dual national man in his 20s has died
- India's foreign minister Sushma Swaraj tweets confirmation of the death of two nationals
The motive for the attack is not clear, but suspicion has fallen on the Islamic State group.
President Recep Tayyip Erdogan blamed terror groups "trying to create chaos". "They are trying to... demoralise our people and destabilise our country," he said.
The banned Kurdistan Workers' Party (PKK) said it was not the work of Kurdish groups. They would "never target innocent civilians", the PKK's Murat Karayilan was quoted as saying.
IS threats: By Rengin Arslan, BBC Turkish, Istanbul
Despite there being no official statement about who might be behind this brutal attack, the finger of blame is being pointed at the so-called Islamic State.
In the last two years of attacks in Turkey, Kurdish militants have mostly targeted military forces and police, while IS is known to target civilians.
IS leaders have threatened Turkey and called on their followers to carry out attacks inside the country.
Turkey began a ground operation against IS as well as Kurdish groups inside Syria four months ago.
Istanbul was already on high alert with some 17,000 police officers on duty in the city, following a string of terror attacks in recent months.
Deadly attacks in Turkey in 2016
10 December: Twin bomb attack outside a football stadium in Istanbul kills 44 people, Kurdish militant group claims responsibility
20 August: Bomb attack on wedding party in Gaziantep kills at least 30 people, IS suspected
30 July: 35 Kurdish fighters try to storm a military base and are killed by the Turkish army
28 June: A gun and bomb attack on Ataturk airport in Istanbul kills 41 people, in an attack blamed on IS militants
13 March: 37 people are killed by Kurdish militants in a suicide car bombing in Ankara
17 February: 28 people die in an attack on a military convoy in Ankara