Weather Phillip Duncan says the lightning tracker detected well over a thousand lightning strikes across Northland and parts of Auckland last night.

Meanwhile heavy rains lashing the North Island have flooded roads and caused landslips, while snow has been blamed for causing a crash further inland.

Inspector Tony Edwards said it was "high tide" on the roads, and advised people to take extra care on the dark, wet roads in the Waikato.

State Highway 25 near Wade Road in Whitianga had some flooding, but was drivable, he said.

"For the next few hours, people just have to drive to the conditions and drive carefully," he said.

Further north, a landslide on SH11 on Lemons Hill near Pahia had reduced traffic to a single lane, he said.

Police reported a large slip on the Napier Taupo Road, SH5, five kilometres north of Te Pohue, which had reduced traffic on the road to a single lane.

Sergeant Mark Oliver said misty conditions had reduced visibility and he advised motorists to be careful.

A slip has also covered part of the southbound lane at the Ashhurst end of the Manawatu gorge tonight, Mr Oliver said.

Drivers were urged to drive to the conditions.

Constant, heavy rain had caused flooding on SH50, reducing the road into Napier to one lane between Tikokino and Ongaonga, he said.

Surface flooding was also causing problems for traffic on SH57, the Old West Road in Linton, south of Palmerston North.

On the central plateau, snow and icy roads contributed to causing a van to roll in SH1 near Waiouru. Two people were injured. Emergency services were at the scene and snow was forecast to continue, Mr Oliver said.

The Automobile Association (AA) reported a slip on SH35 between Tikitiki and Ruatoria, saying the road was reduced to one lane and recommending truck drivers to take care.

Meanwhile, people with caravans, campervans and other high-sided vehicles were being warned to take care in the South Island on SH6 between Harihari and Haast, as strong winds were buffeting the area.

The weather had also prevented a rescue helicopter from picking up an ill woman from a tramper's hut in Hawke's Bay's Kaweka Ranges, so members of the local search and rescue group escorted a medical team into the bush to check on her.

The team would stay with her until morning, then walk her out, police said.