The man then ripped the woman's handbag from her shoulder and ran to a vehicle waiting on the other side of the road.
The pair fled, leaving the woman frightened and shaken but otherwise unharmed, Mr Attwood said.
He said she was able to give a good description of the man, the driver and the car they fled in.
The robber was described as a tall, clean shaven, olive-skinned man in his early 20s. He was wearing dark trousers and a black-hooded sweatshirt with the hood up. The driver, also a man in his late 20s to early 30s, had short, dark, closely shaven hair. He was unshaven and wore a grey top.
He was driving a "brick red" coloured flat deck ute. Mr Attwood said it was an older model with a wooden tray on the back, and it was covered in mud - possibly clay.
"There was one witness to the incident and police are seeking any other people who may have been in the Beach Rd and Carlisle Rd area. We want to hear from anyone who knows the vehicle that was used."
The man did not say anything to the woman, other than demanding her handbag.
Mr Attwood said there had been no similar incidents in the area.
Anyone with information should call Detective Darren Attwood on 09 477 5031 or Crimestoppers anonymously on 0800 555 111.
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North Shore police are asking for help in tracking down a "violent" teenager charged with aggravated robbery using a gun.
Conan Livingstone, 19, failed to appear in court on January 31, resulting in an arrest warrant.
Police describe Livingstone as "a violent man who should not be approached". He is 176cm tall, with a chubby build and distinctive tattoos on his neck, arms and upper body.
Anyone with information on Livingstone's location can call Detective Steve Brewer at the North Shore CIB on (09) 477 5103, or Crime Stoppers anonymously on 0800 555 111.