A woman has been left "very shaken" after being seriously assaulted while out exercising on Auckland's North Shore, police say.

The woman, in her 30s, was exercising on a walking track at Stanley Bay Park in Devonport around 8.30pm on Tuesday when the incident occurred.

It is understood the park has faulty lighting near the pathway because of flooding.

Police said the woman was "understandably very shaken" and support was being offered.

Police are also urging anyone exercising alone to "be alert and aware of your surroundings".

Police are appealing for sightings of a man described as of athletic build, clean shaven, in his 40s and with brown hair.

He is described to have been wearing a black cap, black shorts, a black running T-shirt, and black fabric gloves.

"Sometimes bad things happen to good people, and that's what's happened here," Devonport-Takapuna Local Board chairperson Ruth Jackson said.

"Something bad has happened to a good person and that's just awful.

"I'm really sad that it has happened here."

Lighting on the path at Stanley Bay Park needed repairing and the local board had a project underway to fix it, Jackson said.

"That's already ahead and staff are aware of this incident and looking at the timing of that. It's not a simple replace a few bulbs project, it is a little bit more complex.

"They are going to look at if there is any way to speed that up and bring that forward.

"We need to make sure what we do is done once and done right."

She reminded people exercising alone to remain vigilant, and recommended not using headphones or walking through parks in the dark alone.

But she said there was no need for residents to be fearful.

"From my conversations with police there is no indication for any widespread community alarm or that there was great risk of this occurring again.

"These things are always a shock. It's not something any of us want to have happened."

"I would like to reassure the Devonport community that we are treating this matter seriously and we are doing everything we can to identify the offender involved," Detective Senior Sergeant Nick Poland, of the Waitematā East Investigations Area, said.

Residents around Stanley Bay Park, Jim Titchener Parade, Patuone Place, William Bond St and Calliope Rd areas are being asked to check their CCTV and dash camera footage between 6pm and 9.30pm on Tuesday.

"This incident has occurred on a popular walking track and we believe there are members of the public who would have been in the area at the time and may have seen suspicious activity or a male fitting this description," Poland said.

"We are particularly interested in hearing from a couple who were walking their dog through Stanley Bay Park during the time of the assault."

A team of detectives was making inquiries in relation to the assault, Poland said, and there was an increased police presence in the area.

"If you are exercising alone, we encourage you to be alert and aware of your surroundings," Poland said.

"We ask the public to be vigilant and if you notice any suspicious activity, call 111 immediately."

• Anyone with any information is asked to call police on 105, quoting file number 220209/0390. Information can also be provided anonymously by calling Crime Stoppers on 0800 555 111.