One person is in a serious condition after a car collided with a pole before rolling in Kumeu, west of Auckland.
Emergency services were called to the scene near Wookey Lane and Grivelle St at 4.35pm.
A police spokeswoman said the driver was the sole occupant of the car.
"The person was initially trapped and has reportedly sustained serious injuries," the spokeswoman told the Herald.
Drivers were advised to take extra care while travelling in wet conditions and delays for people travelling in and out of Auckland tonight were to be expected.
Showers are expected to pepper Auckland commuters during rush hour traffic while those further north are in for a soaking.
For Aucklanders leaving the city to head north, traffic is heavy between the Harbour Bridge and the Upper Harbour Highway.
Traffic was also congested for drivers heading into city at Greville Rd and again from Northcote Rd to the Harbour bridge.
On the Southern Motorway, traffic was heavy from the city centre to Takanini. The NZ Transport Agency reported a crash had been cleared near Te Irirangi Dr.
For drivers heading into Auckland from the south, traffic was heavy between Highbrook and the Centre City.
On the Northwestern Motorway, for westbound traffic heavy patches were between St Lukes and Lincoln Rd.
For citybound drivers on the Northwestern, traffic was heavy between Hobsonville Rd and Royal Rd. Waterview tunnel is free-flowing.
Drivers travelling north on the Southwestern Motorway can expect delays between Cavendish Dr and Onehunga.
NZTA has reported a crash blocking the right lane just after Hillsborough Rd on ramp.
For southbound traffic, heavy patches are between Maioro St and Puhinui Rd and slow at the Southern Link.
Traffic incidents elsewhere tonight across the North Island included a van carrying five people which rolled in the town of Waihi in the Bay of Plenty.
St John said they attended the crash at 6.36pm tonight on Tauranga Rd, and transported one person to Tauranga Hospital with moderate injuries.
In Ararimu, on the southern border of the Auckland region, a truck rolled at 2.55pm injuring the male driver in his 20s.
Auckland Westpac Rescue Helicopter attended the scene and treated the driver who suffered multiple injuries and was flown to Middlemore Hospital in a serious condition.
"Although the truck was upright, we could see the windscreen was on the road, and there were scrapes down the side of the vehicle," attending helicopter crewman Greg Brownson said.
While Cyclone Oma is not heading to New Zealand it has contributed to the warm air moving over the country from the tropics.
Electricity companies have put emergency crews on standby today, braced for a possible deluge, as heavy rain warnings are in place for Northland and the Tararua Range.