Kate Malster was paying for her groceries when she saw a woman with a full trolley running full speed towards the exit of the Greenlane Countdown.

Employees from Countdown were shouting "stop, don't do this" to the woman before she exited the store yesterday.

Malster heroically chased the woman into the car park of the Greenlane supermarket, attempting to grab the trolley and telling her to stop before she escaped.

The woman reportedly pushed the trolley to two other people who were waiting at the rear end of a getaway car and loaded the goods.

"I have never seen food go so fast from a trolley into the back of a car ... It was absolutely orchestrated so this definitely isn't their first time," said Malster.

Malster said Countdown staff offered for her to come in and gave her a box of chocolates and water while she tried to calm down.

"I wasn't expecting that in my long weekend," she said.

A police statement said a group of three shoppers left Countdown Greenlane on Great South Rd and did not pay for their groceries at about 2pm yesterday.

Police are making inquiries into the incident and a report of the getaway vehicle breaking down on the western motorway.

"They left in a vehicle and the incident was reported to the police. A short time later a Countdown customer reported seeing the vehicle the group was driving in broken down on the Western Motorway near Khyber Pass," the statement said.

A Countdown spokeswoman said: "We don't tend to comment on stories about thefts in our stores, primarily because it encourages others to try and do the same and unnecessarily puts our team in dangerous situations."