Traffic is set to build up as holidaymakers begin to head home after the festive season.

Those leaving holiday hotspots in the Coromandel are being urged to plan ahead and expect detours with the Thames Coast Rd (State Highway 25) closed between Tararu and Manaia.

The highway was severely damaged by yesterday's monster storm, which washed out parts of the road and left behind rocks and debris.

A detour was in place along SH25, heading east from the Coromandel township, then along SH25A to Kopu.

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The NZ Transport Agency's system manager Karen Boyt said at this stage, NZTA does not think the road will open today.

"In many places seawalls have been damaged and whole sections of the road have been washed away by the storm surges which have also left the road littered with rocks and debris. Other areas of the Thames Coast Rd have suffered upheaval of the road surface as the sea and debris have severely damaged the road surface and the underlying layers," she said.

"Today we are working to assess and categorise the damage to allow us to prioritise repair work. Working with Civil Defence, the first priority is to restore access to Thames Coast communities and open the road to at least one-lane."

There are currently seven crews working along the road to start rebuilding rock walls and clearing debris. There were also three crews working on repairing rock walls and four crews using graders, excavators and broom trucks to clear debris.

"We encourage people who can avoid this area to stay away from SH25 so crews are not impeded and keep highways for emergencies and residents only use," Boyt said.

NZTA contractors have set up a pilot vehicle convoy for residents only to help establish access to coastal communities, which will run from Tararu through to Te Puru. Through traffic will not be permitted.

Boyt said NZTA will share updates on social media if a lane is safely able to be opened later today.

NZTA has urged motorists to drive safely, prepare well and plan ahead to make their holiday journeys safer.

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Traffic has backed up on SH1 northbound heading into Puhoi.

Those travelling back to Auckland from the north on SH1 should also expect heavy traffic between Wellsford and Puhoi today.

According to the NZTA's nationwide map of holiday hotspots and times to avoid travelling, traffic would be at its heaviest in the area until 5pm.

Motorists should avoid the area between 11.30am and 3pm tomorrow when traffic was set to be heavy again.

And the situation wasn't looking much better for those heading back into the city along the Southern Motorway.

NZTA predicted SH1 would be busy at Takanini until 6pm today and between 11am and 5.30pm tomorrow.

The SH2 Maramarua Interchange with SH1 was also predicted to be busy westbound until 5pm today and again from midday tomorrow.

NZTA expected those heading back to the capital on SH1 would face heavy congestion along the Kapiti Coast, following traffic madness in the lead-up to the New Year.

Motorists faced delays of up to an hour on SH1 between Waikanae and Otaki on December 28.

Traffic was set to be at its heaviest along the Kapiti Coast from 2.30pm until 6pm today, and between 1pm and 4pm tomorrow as the last of the holidaymakers return.

Traffic on the Rimutaka Hill southbound between Wellington and Featherston was set to be at its heaviest from 2.30pm until 5pm tomorrow.