Foodstuffs is clearing the air over concerns it's been collecting sensitive information from shoppers without their knowledge.

Our newsroom has confirmed 29 of its supermarkets in the North Island are already using facial recognition technology.

It comes as supermarket crime has skyrocketed, with a 246 per cent increase in serious incidents.

And just last night in Auckland's Sandringham, a dairy worker was fatally stabbed.

Foodstuffs North Island CEO Chris Quin told Mike Hosking the facial recognition data is deleted every five days unless it's someone trespassed or has committed a criminal act in a store.

He says they're trying to protect their customers and staff, as it was only a few weeks ago a customer was stabbed in a Four Square store in St Heliers.