State Highway 1 north of Whangarei and a number of Auckland roads are closed because of flooding.
Police said there is about half a metre of water on SH1 at the Puhipuhi turnoff at Whakapara, and it was still rising.
Trucks were being allowed through but other traffic was being diverted at Hukerenui and Jordan Valley Roads.
Police said drivers should avoid the area and make alternative travel plans.
The heaviest rain has been in the hills north-east of Whangarei, with nearly 200 millimetres at Puhipuhi and falls of up to 40 millimetres an hour.
Several Auckland roads are also closed after heavy rain caused flooding overnight.
Seven roads around Wellsford and Warkworth were closed by flooding, but may reopen this evening if the rain eases.
SH1 at Whakapara north of Whangarei was shut with half a metre of water over the road.
SH16 near West Coast Road in Glorit is also flooded but one lane remains open.
The Transport Agency was also warning drivers north of Auckland to watch out for potholes.
The east coast from Warworth to north of Wangarei has had well over 100 millimetres of rain in the past two days, which caused significant damage to the roads.
The agency said work crews were out on the roads finding and filling in the potholes but motorists should be cautious and drive to the conditions.