An Auckland woman has been left horrified after being overtaken by a vanload of schoolgirls who sat dangling their legs out the door on a stretch of State Highway 1.

Danielle Silich told the Herald she was surprised none of the students were killed as they watched them travel for at least 15 minutes laughing with their legs hanging out of the sliding door.

Silich had forwarded the video to police and Ritchies Coachlines, as well as the school the students attend.

She said they were travelling on SH1 about 10km south of Mangamuka Village, south of Kaitaia, about 5pm yesterday when the van came up behind their vehicle.

"The van drove past us while there was oncoming traffic with the girls' legs hanging out. We were travelling at 100km so they would have had to speed to get past us.

"We were just shocked, really. The girls were waving out to us like what they were doing was cool. We were definitely worried for their safety. I would have expected the girls to know better and the driver to not allow such dangerous behaviour."

Silich said she had contacted the school, which told her the Ritchies vehicle was being driven by a parent.

"Other than the legs hanging out and the first initial dangerous overtaking, the van stuck to the speed limit but the girls' legs remained outside the vehicle through the gorge."

She said it began to rain so the girls closed the door. However, they reopened it once the weather cleared.

"I rang the *555 number as soon as we saw them but didn't see a police car for the rest of the drive."

One of the students also posted the video to Instagram, titled "free aircon".

The Herald is awaiting comment from police and Ritchies. The school's principal and hostel manager have also been contacted for comment.