A two-metre-wide, five-metre-deep hole discovered under the road surface has forced State Highway 10 to be reduced to one lane north of the Kaeo township in Northland.
The hole was found in the southbound lane about a kilometre south of Totara North Road.
Waka Kotahi NZ Transport Agency Northland system manager Jacqui Hori-Hoult said the hole appeared to be a tomo, also known as a collapse hole.
A tomo is caused by build-up of water underground, Ms Hori-Hoult said.
The holes are caused when water seeps into the ground and washes away fine particles, creating a cavity that can eventually collapse soil on top of it. The process can take place within a few hours.
“A culvert close by has collapsed and this may have caused the tomo to develop after recent heavy rain.”
She said NZTA would be assessing the extent of the hole today and then dig out and repair the road.
Ms Hori-Hoult said NZTA advised motorists to take care in the area and watch out for roadside workers.