Three youths are in custody after a security guard was assaulted at a supermarket in Auckland's New Lynn last night

Police say they were called to the Totara Avenue store about 6.30.

Waitemata Detective Senior Sergeant Megan Goldie, says a female security guard confronted an offender, who assaulted her - reportedly with a knife.

She says the security guard's vest and torso were penetrated, but she escaped serious injury.

Goldie says the guard was taken to hospital, and is being supported.