Motorists from outside Northland are being asked not to travel to the region today, as crews work to repair flood-damaged roads.

Thunderstorms swept through Mangawhai at the border with Auckland on Friday, with floodwaters stranding hundreds of people.

They were escorted to State Highway One yesterday because of damage on many local roads between Kaiwaka, Mangawhai and Waipu.

Cove Road is open to residents from Waipu only in the north, with the Lang's Beach bridge being assessed by a structural engineer.

The Kaiwaka to Mangawhai Road is closed near the Hilltop Road intersection and Devich Road is closed at the bridge.

Waka Kotahi says light vehicles can use SH12 and the Paparoa-Oakleigh Road to get to Whangārei but heavy vehicles must use SH12 and SH14 between Brynderwyn and Whangārei (via Dargaville) only.

Road crews are trying to make as much progress as possible in the area before the working week begins, with some local roads expected to reopen later today.

SH1 at the Brynderwyn Hills and Waipu remains closed due to large slips, and motorists from outside the region are being asked not to travel to Northland, unless it is necessary.

Mayor pleads for help from central government

Whangārei Mayor Vince Cocurullo said the damage caused by Cyclone Gabrielle to roads in Northland was significant and would cost at least $120 million to fix.

"We would just love central government to come to the party and actually get the Brynderwyns back open or even to - what we would really love - is a four-laning between Whangārei and Auckland."

The additional rain on Friday night meant costs would continue to rise, he said.

"We are also realistic that there may be some more damage happening to the roading network; we have got the contractors out there at the moment, the team's out there keeping a close eye on the roading," he said.

"But it is a major issue when you constantly have more and more rain."

Cocurullo said road crews were working around the clock to restore access.