Prime Minister Chris Hipkins has officially opened the new Pūhoi to Warkworth motorway heading north from Auckland.

Watch the PM speaking here:

After joining other officials to cut the ribbon on the $880 million Ara Tūhono - Pūhoi to Warkworth - motorway Hipkins said it was a "really significant day for the north".

The motorway was a "vital transport link between Auckland and the Northland Region", he said, and while there was still more work to do on it, today's opening was a milestone worth celebrating.

The 18.5-kilometre stretch of motorway was built as a partnership between Waka Kotahi and the Northern Express Group and will open to the public shortly, with only finishing works outstanding and expected to be completed over the next few months.

More than 35,000 vehicles are expected to travel the stretch of road every day, including 1300 trucks.

Hipkins said the roading project was one of the biggest the country had seen in recent times, with thousands having worked on it and thousands of others standing to benefit from it.

The weather events of earlier in the year had shown how "vulnerable" some of New Zealand's roading network was and the new motorway would be a "great thing for the community", he said.

"This is a really significant step in the right direction in terms of getting a more resilient and more reliable and a safer road up network up here."

Planning and consenting work was "well advanced" for the next section of the road, he said.

"We certainly acknowledge the vital importance of this section of road.

"Linking the Auckland Region to the Northland Region, this is the main lifeline, this is the main highway - we need to make sure that we're investing in it."

Photo: Stuff / Jason Dorday

Labour had been wrong to call the motorway the 'holiday highway' he said, though he stood by his party's earlier criticism that it was wrong that "all of the funding was being directed into roads of national significance and away from maintenance and away from local roads".

"We're still seeing the long-term effects of that now in the number of potholes we've got in our roads and the maintenance that just wasn't done during that period when all the funding was being diverted to roads of national significance," he said.

"The reality is we need to do both, we need to invest in new roads, but we've also got to make sure we're maintaining the existing roads that we've got."

Both Ara Tūhono and the $62m Te Honohono ki Tai Matakana Link road were due to open to motorists "very soon" Associate Transport Minister Kiri Allan said, though exact times had not been announced in a bid to avoid traffic building up.

"Waka Kotahi says [announcing the opening times] does increase the chance of people coming up and causing some disruption."

Together with the Matakana link road project, the new stretch of motorway will allow motorists heading to Matakana and the coast to bypass an often-congested intersection in Warkworth.

The link road, Te Honohono ki Tai, was finished and ready to open.

Auckland Transport (AT) chief executive Dean Kimpton said the road would reduce traffic through the Hill Street intersection at Warkworth by about half.

"It'll really free it up and allow people to move more quickly... people will enjoy the difference. We'll have bus services in place and you'll see increased frequency and reliability."

Kimpton said the Warkworth Community Transport Hub would be the logical place to park and ride, freeing up car park spaces in the township for business and retail visitors.

"The Hub opening was meant to coincide with Te Honohono ki Tai Road and Ara Tūhono - Pūhoi to Warkworth, but was finished early. Once bus commuters realise there's plenty of free parking with new facilities, the Hub will come into its own."

The 995 bus between Wellsford and Hibiscus Coast Station in Silverdale will run along the new motorway.

The link road was 1.35km-long and connected Matakana Road and SH1 just north of Warkworth. It featured a bridge as well as walking and cycling facilities.

The link road cost $62m to complete and was jointly funded by AT and Waka Kotahi.

Wellsford-based Wharehine Construction managed the build, which took just under three years to complete, including delays due to Covid-19 and storms.

The name Te Honohono ki Tai was gifted to the project and the road by Warkworth-based iwi Ngāti Manuhiri.

It means "from the land to the sea", and reflects the pathway Te Honohono ki Tai Road takes from SH1 to Matakana Road.

This story was originally posted by Radio New Zealand