Police are investigating the armed robbery of a convenience store at Ultimo yesterday.

Just before 11.30am (Sunday 27 March 2016), a man with his face covered by a medical mask entered the store on Bulwara Road and confronted the attendant, a 29-year-old woman.

The man produced a knife and a hammer and demanded money from the attendant who locked the cash register.

The man then stole a number of cigarettes from behind the counter and again demanded the attendant open the til.

The woman complied with the demand and the man ran off. He was last seen running west along Bulwara Road.

Police were alerted and officers from Sydney City Local Area Command attended and established a crime scene.

An investigation is underway and officers would like to speak with a man who may be able to assist with inquiries.

He is described as being approximately 165 to 170cm tall with a medium build and had his face covered by a white medical mask.

He was last seen wearing a grey-coloured hooded jumper with a navy blue front, dark-coloured tracksuit pants and black shoes.