Turkish police stand guard outisde the Reina nightclub by the Bosphorus, which was attacked by a gunman, in Istanbul, Turkey, January 1, 2017. [Photo/Agencies]

The gunman was on the run after slipping out of the nightclub in chaos, leading to a manhunt by police.

The assailant armed with a "long-range weapon" was seen changing his ammunition clip several times in the assault and heard speaking Arabic "Allahu Akbar" (God is greatest).

NTV broadcaster said the gunman fired between 120 and 180 rounds in the seven-minute attack, during which some revellers even jumped into the freezing waters of the Bosporus to escape.

"Unfortunately, (he) rained bullets in a very cruel and merciless way on innocent people who were there to celebrate the new year and have fun," Istanbul Governor Vasip Sahin told reporters.

There was no immediate claim of responsibility for the attack or comments from the Turkish authorities on the possible identity or motives of the gunman.

Turkey has been hit by around 30 bombing attacks over the past one and a half years, in which more than 400 people lost their lives, prompting calls for steps to revamp the intelligence units and reduce polarization in society to better counter the scourge of terrorism.

Ankara has blamed the terror attacks on its soil mostly on the outlawed Kurdistan Workers' Party (PKK) and the Islamic State (IS) group that is wreaking havoc in neighboring Iraq and Syria.

PKK leader Murat Karayilan was quoted by the Firat news agency as saying that no Kurdish force was involved in the attack.

Only days ago, an online message from a pro-IS group called for attacks by "lone wolves" on "celebrations, gatherings and clubs."

Abdullah Agar, a security analyst, saw both the target and the perpetrator as being selected "very attentively."