A long-board rider who overtook a truck-and-trailer unit at up to 100km/h on the Bombay Hills expressway has been labelled stupid and idiotic by traffic police.

Canadian Andrew Chapman posted a video on Facebook showing him and five friends using the devices - similar to surfboards but with wheels - on SH1.

The group travelled the North Island for two weeks in summer on a long-boarding tour as part of a month-long world trip.

The video surfaced yesterday, after being discovered by blogger Cameron Slater and uploaded to YouTube.

The footage shows six riders setting off from near the top of the Bombay Hills and Chapman filming as he skates behind the others.

The group proceed on to the Waikato Expressway, with Chapman cruising behind a car and the truck-and-trailer unit.

He gathers speed, passes three others and moves into the left lane to pass the truck - for which the limit on the open road is 90km/h.

Chapman passes a fourth long-boarder, who is not wearing shoes, before taking the State Highway 2 offramp and coming to a stop.

The distance travelled is about 2.5km.

Acting Inspector Grant Miller of the Auckland motorways police said that although it was not illegal to ride such boards on an expressway, riders - who are defined as pedestrians - could still face charges such as failing to keep to the left of the road.

They could also be charged with careless driving, which incurs a maximum fine of $3000 or, if a person is hurt or killed, up to $10,000 and/or a three-year jail term.

Waitemata road policing manager Superintendent John Kelly said of the long-boarders: "I would describe it as an incredibly stupid act. They've got no real protection.

"What concerns me about that is the speed they get up to and the lack of control they've got. They've got no brakes.

"If something goes wrong in front of them, they're terribly exposed to risk.

"There's a crash on the road in front of them, for example, and they can't stop; the only way is to fall off or leave the road and crash into something."

When the Herald described the footage to Counties Manukau road policing manager Heather Wells, she found it hard to believe.

"I just can't see that it's possible, and if it is, they're jolly stupid. All they have to do is come off and they would kill themselves.

"They get speed and it doesn't take much to fall off and hit their head on the kerb and cause permanent brain damage.

"If it's real, he [Chapman] is an idiot. If any of the police staff had seen him, he definitely would have been taken off the road."

Chapman travels the world skating to promote the long-board manufacturing company Landyachtz, based in Vancouver.