The NZ Transport Agency will make a decision late tomorrow on whether it's safe to re-open State Highway 1 on the Brynderwyn Hills in Northland.

The main road transport link between Northland and Auckland was closed yesterday because of an underslip on the southern side of the hills after a weekend of heavy rain,

Transport Agency's Regional State Highways Manager, Jacqui Hori-Hoult said they had originally thought they would have to keep the highway closed until the end of the week.

"It may now be possible to re-open the highway tomorrow afternoon to light vehicles only," she said.


"Repairs might be easier than we had originally thought. However, we do need to wait another day to be absolutely sure that it is safe to have traffic using this section of SH1 again."

Ms Hori-Hoult said if experts give the all clear, one lane would be re-opened to motorcycles, cars and light commercial vehicles only.

"The critical period will be tonight and tomorrow. We can understand people wanting the highway re-opened as quickly as possible, but if we don't get that all clear the road remains closed."

Ms Hori-Hoult said because of the location and size of the underslip, it was still too risky to re-open the Brynderwyns to heavy vehicles until full repairs were completed.

Two alternative routes were available for all traffic travelling between Northland and Auckland.

People driving north are advised to use SH12 and the Paparoa-Oakleigh Road. Those heading south can travel through Waiapu and Mangawhai.

The detours will add between 30 and 40 minutes to travel times, NZTA said.