A house being transported on State Highway 16 near Kumeu has fallen off a truck, blocking the road and forcing the highway's closure.
Traffic is reportedly backlogged at the site of the fall and NZTA has advised the road will be closed for a long period this morning.
The incident occurred 100m north of the Old North Rd roundabout around 5.50am.
The road is blocked in both directions between Old Railway Rd and Old North Rd. No one was injured, police said.
Auckland resident Greg Martin said he watched the house fall off the back of the truck as it entered a corner by the Kumeu vegetable store.
He had been following the truck for some time and said it seemed to be stable.
The structure that had fallen on the road was one of two sections of the house being transported on two trucks, he said.
The house had slipped when the second truck went into a tight corner by the Kumeu Produce store.
"The front truck went through ok. Then the second one sort of flipped off and went in slow motion.
"It crashed on to the road and slid from the back first."
He said the house had not crumbled on impact but it looked like there was significant damage to it.
Motorists were being asked to avoid the area or expect delays.