A large slip that has cut off State Highway 1 at the Brynderwyns could be cleared and the road reopened by the end of the week, transport officials say.
The underslip, about 20m long in the northbound lane on the south side of the hill, had fallen away leaving an 8m drop to the ground below and happened less than 48 hours after the reopening of SH1 south of Kawakawa following round-the-clock work on a temporary bypass.
The NZ Transport Agency said it plans to have SH1 on the Brynderwyn Hills re-opened to all vehicles at the end of this week, weather permitting.
"We were hopeful of possibly getting one lane open sometime (yesterday) afternoon, but detailed inspections today indicate that the under-slip is a lot bigger than we originally thought," NZTA spokeswoman Jacqui Hori-Hoult said.
"We have removed the loose soil and are starting work to stabilise this section of the highway that encroaches into the southbound lane hanging over an 8-m drop.
It's just not safe enough to open even just one lane to light traffic."
She said there are two alternative routes available for all traffic travelling between Northland and Auckland. People driving north are advised to use SH12 and the Paparoa-Oakleigh Rd.
Those heading south can travel through Waipu and Mangawhai, with the detours adding between 30 and 40 minutes to travel times.
Meanwhile, on a diversion around the Brynderwyn Hills a woman was airlifted to Whangarei Hospital after a collision with another vehicle towing a trailer.
Whangarei police spokeswoman Sarah Kennett said the woman was driving east on Paparoa Valley Rd and had stopped to give way to an oncoming vehicle crossing a single lane bridge near Ararua Rd, about 1.50pm on Monday.