A woman has described the terrifying moment she and her son were robbed at a supermarket.

The woman, who wishes to remain anonymous, was with her 19-year-old son on Christmas Eve at the petrol station at the Asda in Hollingbury, Brighton, when the attack happened.

The pair had been on their way to spend Christmas with family and had stopped to get fuel at the garage in Crowhurst Road.

After paying, the woman was putting items away in her car when a man approached the vehicle, opened the driver’s door and began pulling at her son’s bag before punching him in the face.

“We were about to go to my parents and someone opened my car door and punched my son in the face,” she said.

“We came out after paying and I was putting things in the back of the car. I heard a man’s voice and he said ‘all right mate’ to my son and then started pulling at his bag and then punched him in the face.”

They feared the attacker, who made off with the teenager's bag, might have had a knife.

“When my son ran after him the guy began to pull something out of his waistband,” said the woman.

“My son thought it was a knife.”

The woman said she cannot stop thinking about the attack.

“It’s terrifying,” she said. “I keep playing it over and over in my head.”

Sussex Police are investigating the incident and are searching for the robber.

A force spokesman said: "Police responded to a report of a robbery and assault at Asda petrol station in Crowhurst Road, Hollingbury, on December 24 at around 4pm.

"A man reportedly opened the passenger side of a parked car and grabbed a backpack from the passenger before assaulting him, causing minor injury.

"The suspect then made off with the bag.

"Enquiries to locate the suspect are ongoing and anyone with any information or dashcam footage is asked to report it online or call 101 quoting 662 of 24/12."