Thieves are using a terrifying tactic to snatch bags from unsuspecting shoppers - and it's been captured on CCTV.

Counties Manukau police warn that thieves are blocking parked cars from reversing out of their car parks, before opening passenger doors and grabbing handbags from the front seat.

Botany and Papatoetoe have been worst hit by the crime spree, said Sergeant Nicolas Jensen.

"The method in which these crooks offend, they'll park their vehicle behind yours. The passenger will exit their vehicle, run to yours, steal your handbag and they're gone."

Police were still investigating, Jensen said. "We'd like to reassure the community that we take these matters very seriously."

Stolen cars are being used to commit the crimes but CCTV from petrol stations and dairies has captured video of some of the alleged offenders.

Anyone who recognises the people in the video should call 105 and quote file number 210502/1803, he said.

Jensen also offered some tips on how to stay safe. "Don't carry heaps of cash on you; when you get in your car, lock your doors. Avoid being a target. Put your handbag under your front seat."

If people did find themselves with a thief opening their car door, they should keep themselves safe and let police handle the criminals.

"Don't chase the offender. Call 111, get a good description of the offender, and let us deal with it," Jensen said.

Today's police warning follows the case of a woman who was injured after a man tried to steal her car in a "violent" assault in a New Lynn shopping mall a fortnight ago.

Police said the 69-year-old had parked her car in the ground-level car park of the Lynn Mall shopping centre about 10.30am when a man assaulted her, took her cellphone and tried to steal her car.

The victim has fought back, causing the offender to exit the vehicle and attack her a second time.

"A member of the public has pulled up to see what is happening which has disturbed the offender, who has quickly fled the scene on foot with the victim's cell phone," Detective Senior Sergeant Mike Frost said at the time.

The victim required medical treatment for injuries suffered in the attack.