A house which fell off a transporter, closing State Highway 16 in north-west Auckland, happened in slow motion, an eyewitness says.

The incident occurred about 100 metres north of the Old North Rd roundabout, near Kumeū, at 5.50am on Tuesday.

The manager of the removal company transporting the house said the driver may have lost concentration momentarily, and he did not believe the house was damaged in the fall.

West Auckland resident Greg Martin was three cars behind the pilot vehicles when he saw a truck carrying a smaller piece of the house drive through the roundabout.

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Martin said he could see the trailer begin to wobble and watched in slow motion as the house fell onto the road, instantly blocking it.

CHRIS MCKEEN/STUFF Police at the scene of a house falling off a truck onto SH16.

The house fell onto the right-hand side of the road, while the truck remained on the left, he said.

"It was a bizarre thing to see, I've never seen anything like that before.

"It was a surreal kind of thing to see. You don't expect to see a house fall off the back of the truck first thing in the morning and how slowly it happened too."

CHRIS MCKEEN/STUFF The house blocked SH16 at Kumeū for more than three hours on Tuesday morning.

Martin said the drivers involved quickly jumped out of their vehicles to assess the situation and turn vehicles around.

He quickly turned around to get to Kumeū through back roads as he knew "chaos would ensue".

Craig Walker, of Craig Walker Building Removals, confirmed it was his company moving the house.

Walker said he was currently out of Auckland but would be investigating the incident when he arrived back on Tuesday afternoon.

From talking to the team, Walker said he understood it was a user error and the driver may have lost concentration momentarily.

There was no damage to the house from what he understood.

CHRIS MCKEEN/STUFF Removers working to clear the house from the highway.

The road was initially blocked in both directions but the house had been recovered by 9.10am, the New Zealand Transport Agency said.

A police spokesperson said no-one had been injured as a result of the house falling.

Police were no longer at the scene as of 9.30am but the Commercial Vehicle Safety Team had attended and would be making follow up inquiries into the incident, the spokesperson said.