A man brandishing a metal hammer attacked a woman inside her car after she stopped on the side of the road to adjust her radio, police say.

Hamilton Police have launched a manhunt for the offender, described as being Maori and in his early 20s.

The attack happened at about 12.30pm yesterday on Tramway Road in Enderley, police said.

The 27-year-old woman had been driving along the road before pulling over to adjust her stereo.

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She was approached by an unknown man brandishing a large metal hammer, police said.

"The man assaulted the woman with the hammer before she exited the vehicle and ran towards the intersection of Tramway Road and Powells Road."

A member of the public came to the woman's aid at that point and the offender ran down a nearby alleyway.

The woman suffered minor injuries in the attack.

The offender was wearing a hooded camouflage-styled sweatshirt and black skinny jeans.

Can you help? Anyone with information is urged to call Hamilton Police on: (07) 858 6200 or CrimeStoppers anonymous on: 0800 555 111.