A woman has been caught urinating in a car park near Auckland's Westhaven Marina in front of an "appalled" witness and his children.

She and her companions then sped off while shouting insults at the person who whipped out their phone to film the "absolutely disgusting" act. There was a public toilet just 20 metres from the car.

Scott, who only wanted to be identified by his first name, said he had been walking with his kids on the wooden walkway on Westhaven Dv, near the Auckland Harbour Bridge yesterday when the woman pulled up in a car with three friends.

"It was a beautiful Sunday morning, blue sky, everyone was out walking," he said.

"There was lots of people around, lots of kids, lots of dog walkers, lots of elderly.

"Then the car pulled over and one of them got out."

Telling the woman it was "absolutely disgusting", Scott began filming and said the woman was poised to defecate.

"She was pooing ... and before it went on the ground, she saw me, got up and pulled her pants up over it and got back in the car," he said.

"It was despicable and appalling."

As the car drove off, the occupants then called Scott a "f*** white c***", he said.

The act took place just 20m from public toilets.

Scott said he could see a wine bag in the car's back seat.

He said that was not what you want to see when out walking with your kids.

"That area is just an absolutely beautiful, stunning part of Auckland, and you get these hooligans come in on a Sunday morning and do that - it is just inappropriate."

He said he had reported the incident to police.