State Highway 1 through the Brynderwyn Hills, between Kaiwaka and Waipū, has been closed after heavy rain caused some slips onto the road.

"We have crews on site working to clear the road as quickly as it is safe to do so," NZTA said in a statement just after 3pm.

The agency said they were monitoring the hill for any more movement and would only reopen the road when it is determined to be safe.

Another update was due around 6pm, the agency said.

The route is Northland's main connection with the rest of the country, and only reopened in June after a four-month closure due to earlier slips.

NZTA project director for Northland recovery Mark Ware said heavy rain overnight had caused the slips.

Machinery was on site to move the soil, he said.

There was a detour in place for cars and other light vehicles detour via Nova Scotia Drive, Cove Road, Garbolino Road, and Kaiwaka-Mangawhai Road.

In an earlier statement, NZTA said because it was a "significant slip", the detour was not suitable for trucks; instead, they needed to detour via State Highway 12 and SH14.

"We have been advised by our council partners that Paparoa Oakley Road is unsuitable for freight at this time as there has been a significant under slip on the road."

NZTA would continue to monitor the routes and provide updates.

It advised drivers to check road and weather conditions before they travelled.