ISTANBUL, Jan 1 (Reuters) - At least 35 people were killed and 40 wounded when an attacker opened fire on New Year's revellers at a nightclub in Istanbul on Sunday, Istanbul Governor Vasip Sahin told reporters.

The attacker shot a police officer and a civilian as he entered the club in the Ortakoy district of Istanbul before opening fire inside the building, Sahin said, in what he described as a terrorist attack.

(Reporting by Humeyra Pamuk and Ece Toksabay; Writing by Nick Tattersall)