ISTANBUL, Jan 1 (Reuters) - An attacker shot at police officers outside an Istanbul nightclub early on Sunday before entering and opening fire at random inside the building, where around 500-600 people were celebrating the New Year, broadcaster NTV said.

Police special forces and explosives experts were still searching the club in the Ortakoy district of Turkey's most populous city, an NTV correspondent at the scene said. The whereabouts of the attacker was unclear.

(Reporting by Humeyra Pamuk; Writing by Nick Tattersall)