An Uzbek gunman who killed 39 people in an Istanbul nightclub on New Year's Day told police he had to change target at the last minute to avoid heavy security and acted with direct orders from Daish in Syria, a newspaper said on Wednesday.

The gunman, named by the authorities on Tuesday as Abdulgadir Masharipov, had initially been told to attack the area around the central Taksim square and said his instructions came from Raqqa, a Syrian stronghold of Daish, the Hurriyet newspaper cited him as saying in police testimony.

"I came to Taksim on New Year's Eve but the security measures were intense. It was not possible to carry out the attack," he was quoted as saying.

"I was given instructions to search for a new target in the area. I toured the coast at around 10pm with a cab," he said, referring to Istanbul's Bosphorus shore where the Reina nightclub is located.

"Reina looked suitable for the attack. There didn't seem to be many security measures."

Hurriyet did not say how it obtained the testimony and Reuters was not immediately able to verify the report.

Masharipov was caught in a police raid late on Monday in Esenyurt, a suburb on Istanbul's western outskirts, following a two-week manhunt. He was captured with an Iraqi man and three women from Africa, one of them from Egypt.

On January 1, he shot his way into the exclusive nightclub and opened fire on New Year's revellers with an automatic rifle, throwing stun grenades to allow himself to reload and shooting the wounded on the ground.

Daish claimed responsibility the next day, saying the attack was revenge for Turkish military involvement in Syria. Turkish troops entered Syria last August to push Islamic State away from the border and halt Kurdish militia advances.

Like many cities around the world on New Year's Eve, Istanbul had taken additional security measures, deploying 25,000 police officers to try to thwart attacks after a year of bombings by Daish and Kurdish militants.

Istanbul Governor Vasip Sahin said on Tuesday that Masharipov had admitted his guilt and that his fingerprints matched those at the scene.

Sahin described him as well-educated, able to speak four languages, and said he had received training in Afghanistan.