Police are investigating after a fast food outlet on the Central Coast was robbed at knifepoint overnight.

About 9.30pm (Monday 14 January 2019), staff at the restaurant on West Street, Umina Beach, were preparing to close for the night, when a man came through the back door.

Officers have been told the man, who had his face partially concealed, threatened staff members with a large knife and demanded money.

The staff handed over a sum of cash before the man fled on foot.

Officers from Brisbane Water Police District arrived a short time later, establishing a crime scene that was examined by forensic specialists.

As their investigations continue, they would like to speak with a man described as being aged in his mid-30s and about 183cm tall. He was wearing a grey hooded jumper, dark blue pants and black boots at the time.