It was supposed to be a celebration welcoming in a new start, after a trying, bloody year in Turkey.
But a New Year's bash in an upscale club in Istanbul's Besiktas municipality turned into yet another bloodbath, with at least 39 revelers killed, and almost 70 people hospitalized after an unknown number of attackers stormed the club and started shooting.
"We were having fun, at first we thought it was a fight then there was a lot of gunfire," eyewitness Yunis Turk told CNN after police secured the Reina nightclub in the neighborhood of Ortakoy.
"After the gunfire everyone started to run toward the terrace. We ran as well. There was someone next to me who was shot and fell on the floor. We ran away and hid under the sofas."
Some people jumped into the Bosporus, he said, a testament to the panic that engulfed the nightspot -- it is freezing in Istanbul but people were willing to leap into the frigid water to escape the panic.
"For ten minutes there was gunfire and then for another five minutes they were throwing bombs, fired a bit more, then left," Turk recalled.
Turkish Deputy Prime Minister Numan Kurtulmus told CNN sister network CNN Turk that the attacker is a lone assailant and that the authorities "are trying hard" to identify and apprehend the person in order to investigate any ties to terror groups.
He said that security forces are analyzing CCTV footage.
"I hope we will shortly identify the attacker and find who is behind it," he said.
Latest developments
The death toll from the Reina nightclub shooting has risen to 39 The number of injured is at 69; "Four of them are in critical condition -- one very critical," says Interior Minister Deputy PM tells CNN Turk the attacker is one person and "we are trying hard to catch" them No claim of responsibility has yet been made US, Turkish officials say incident is a terrorist attack
First terror attack of 2017
Turkish President Recep Tayyip Erdogan released a statement via the semi-official Anadolu agency, offering his condolences to the families of the victims.
In the statement he said that those who attack the "serenity" of Turkey were trying to sow "chaos" but that the nation would not allow "this dirty game," by uniting and remaining calm.
Russian President Vladimir Putin expressed condolences to Erdogan following the deadly attack in Istanbul and said "our common duty is to respond decisively to the terrorist aggression," according to a statement released by the Kremlin.
Putin also said Russia was and would remain Turkey's ally in the fight against "this evil."
Despite no group yet claiming responsibility, Turkish authorities quickly characterized the attack as the work of terrorists.
"We are face to face with a terror attack," Interior Minister Suleyman Soylu told reporters Sunday morning.
Twenty-one of the dead have been identified, he said. Of those, 16 were foreign nationals and five were Turkish.
US officials also called it a terrorist attack, making it the first of 2017.
Soylu also said that "the efforts to locate the terrorist are ongoing. Security forces have begun the necessary operations. God willing soon (the attacker) will be apprehended."
Around 1:15 a.m. Sunday, the gunman shot a police officer who was guarding the front gate at the Reina nightclub, killing him, Istanbul Governor Vasip Sahin said.
"He entered the club and attacked innocent people who were there to celebrate the new year. It was a cruel, cold-blooded act," the governor said.
'Crazy people shooting everything'
Witnesses in the club said they heard a loud noise, then a security officer told everyone to get out.
One victim said he didn't know how many attackers there were, but he saw one person and hid.
"I got shot in the (expletive) leg, man," he told journalists in English as he was taken into an ambulance. "These crazy people came in shooting everything."
A security camera captured the moment a gunman dressed in dark clothing dashed into the Reina nightclub as bullets ricocheted in the street.
The assailant, who has not yet been identified, opened fire inside the high-end nightclub in the busy Besiktas neighborhood, according to Turkish state-run news agency Anadolu.
Besiktas, on the European shore of the Bosporus, is known for its expensive, upper-middle class neighborhoods. The popular area had been under heavy police security for new year celebrations.
Ortakoy, where Reina is located, is a vibrant seaside neighborhood that caters to a wide range of people, from the uber-rich who party at clubs like Reina, to students who buy stuffed baked potatoes from vendors along the Bosporus.
Reina itself is one of the first clubs to open along the famous strait and remains a touchstone for Istanbul's exclusive nightlife. It boasts a classic Istanbul view.
Several analysts said the attack looked more like a jihadist-inspired attack.
"In terms of the soft-target aspects of this attack, it's a youthful place, a bar that's pretty well-known in particular to expats. It's sort of the lively area of Istanbul, and especially on New Year's Eve night -- all of those have hallmarks of ISIS-inspired, if not directed attacks to maximize casualties and get a lot of news around it," said Juliette Kayyem, CNN's national security analyst.
Turkey's recent tumult
Turkey has endured a recent wave of terrorist attacks, leaving many people wary.
"This attack is, of course, a horrible development, but not shocking to many Turks who chose to stay inside this New Year's Eve," said Aykan Erdemir, former member of the Turkish Parliament.
"Turkey is known to host these big parties to celebrate New Year's, but this year most citizens were wary of Islamist attacks so they chose to celebrate it at home with their friends."
He said the attack seemed similar to what happened at the Bataclan, a Paris concert hall that was attacked by gunmen in 2015.
"This is an attack on the Western lifestyle. This is an attack on Turkey's secular, urban way of living. And this will simply fuel the ongoing cultural clashes, the ongoing polarization in Turkey," Erdemir said.
The United States condemned the attack.
"That such an atrocity could be perpetrated upon innocent revelers, many of whom were celebrating New Year's Eve, underscores the savagery of the attackers," National Security Council spokesman Ned Price said in a statement.
The US State Department said the attacks like this one on its NATO ally "only reinforce our strong determination to work with the government of Turkey to counter the scourge of terrorism."
The US Embassy in Turkey warned citizens to avoid the area where the attack occurred.
A violent year
Turkey faces numerous battles across different fronts. Not only have the Syrian conflict and refugee crisis spilled over into Turkey, but Turkey is also battling ISIS and Kurdish militants.
Both have staged attacks in Turkey, which is still reeling from a bloody and failed military coup in July.
ISIS is suspected in a June attack at Istanbul's Ataturk Airport that left 44 people dead and an explosion at an August wedding, not far from the border with Syria, that killed at least 54 people.
Meanwhile, Turkish security forces clash on an almost daily basis with Kurdistan Workers Party (PKK) militants, mostly in predominantly Kurdish parts of southeastern Turkey.
A pair of bombings in Istanbul killed 44 people and wounded 155 others December 10 in an attack by a breakaway group of the PKK. The two explosions occurred after a heavily attended soccer game at Besiktas Vodafone Arena.
On December 17, a car bomb exploded near a public bus, killing 13 soldiers in the central province of Kayseri. Three days later, a gunman assassinated Russia's ambassador to Turkey at an Ankara art gallery.
CNN's Steve Almasy, Gul Tuysuz, Nadeem Muaddi, Laura Koran, Joel Williams and Steve Brusk contributed to this report.
