Police Minister Stuart Nash has been illegally driving around Hawke's Bay for more than a month - his MP for Napier vehicle had an expired registration.

An eagle-eyed local spotted the blunder when Nash's car was parked, and shared a photo on a Facebook community page.

Nash said he had only spotted his registration was a month and a half out of date after a family member pointed it out.

"I had no idea it had expired but thankfully a family member gave me a heads up earlier today [Wednesday] and I renewed it online," Nash said.

"The registration of my MP for Napier vehicle is now current, but the license label for the windscreen has not yet been updated."

According to NZ Police the only acceptable reason for using your vehicle without a valid registration would be to take it to the garage for a warrant of fitness test.

The fine for an expired registration or WOF is $200.

Nash said he wasn't aware of any reminder being sent out to renew his rego, but would be more vigilant in the future.

"I'm not aware that any infringement notice was issued but I'll keep an eye on the post."