People heading out of Auckland for the long anniversary weekend are being warned they could face long delays.
Heat and traffic have caused SH1 to "react" near Johnstone's Hill tunnel south of Warkworth, forcing trucks to block the road as they cool it with water.
Meanwhile a truck has broken down just after Massey Road on the Southwestern Motorway SH20 about 5.45pm, forcing closure of the left southbound lane.
It was cleared 20 minutes later but NZTA warned motorists to expect delays.
The Transport Agency said drivers leaving the city this afternoon and tomorrow morning were likely to hit congestion.
Theading north on State Highway 1 could consider taking SH16 instead, to avoid the usual bottlenecks around Pūhoi and Warkworth.
People heading south or to the Coromandel were urged to travel outside of peak times.
Auckland Transport Operations Centre manager Rua Pani said drivers should be patient.
Traffic cams show slowing traffic just before 3pm. Clockwise from top left: SH20 Massey Road; southbound on SH1 Market Road; SH1 South Eastern Highway; SH1 Greenlane interchange. Photo: NZTA
"Trying to overtake to get in front of one or two cars is not going to add any great value to their journey and it creates even more congestion.
"If everybody just held back and were more patient they'd probably get there faster."
Ms Pani said roads heading into the city were expected to be busy on Monday as people head home.
Weather
Meanwhile, MetService is forecasting a warm and muggy long weekend for the top of the North Island.
MetService meteorologist Lisa Murray said Auckland will be hot and muggy over anniversary weekend.
"For Auckland in particular it looks like really muggy weather, where temperatures are going from about 26, 27 during the day down to about 20 during the night," she said.
"And 20's a really warm, muggy temperature for trying to get some good sleep."
Humidity could hit almost 100 percent and the skies are expected to be mostly cloudy.
Over the rest of the country, this weekend looks set to be the hottest of the year so far.
MetService is forecasting more than 30-degrees for the eastern North Island, and mid-to-high-20s for the rest of the country.
"Sunday, Monday, Tuesday looking really hot in eastern parts of the country," Ms Murray said.
She said Blenheim could hit 34C on Monday.
For those staying in Auckland, a number of events are being held around the city, and tens of thousands are expected to turn out.
The events include:
- Auckland Live Sounds of Summer in the Square - 10-27 January, Aotea Square
- International Buskers Festival - 25-28 January, throughout the CBD
- Auckland Latin Fiesta - 26 January, The Cloud
- Ice Cream Sundae Market - 27 January, Silo Park
- Ports of Auckland Seeport Festival - 26-28 January, Captain Cook Wharf
- St Jerome's Laneway Festival - 28 January, Albert Park
- Vector Lights - 25-29 January, Auckland Harbour Bridge