More pain is in store for motorists after a huge truck fire caused motorway mayhem and left behind a cocktail of toxic chemicals this morning.

The burnt-out truck has to be removed after fire engulfed it beside State Highway 1 (SH1) in Paremata, near Porirua north of Wellington.

Fire crews battle a blaze on a trailer unit loaded with aerosols and thinners. Photo / SNPA / Derek Quinn
Fire crews battle a blaze on a trailer unit loaded with aerosols and thinners. Photo / SNPA / Derek Quinn

A "putrid smell" was lingering in the air and lengthy diversions were in store, the New Zealand Transport Agency (NZTA) said.

The highway was being closed again to get the truck and trailer out."...There's going to be disruption throughout the day," an NZTA spokesman said.

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The agency planned to close all the highway's southbound lanes for five hours.

Fire crews battle a blaze on a trailer unit loaded with aerosols and thinners on the north bound lane on SH1 at Paramata causing major traffic delays. Photo / SNPA / Derek Quinn
Fire crews battle a blaze on a trailer unit loaded with aerosols and thinners on the north bound lane on SH1 at Paramata causing major traffic delays. Photo / SNPA / Derek Quinn

"This is to enable the emergency services and contractors to clear the burnt out truck and its flammable goods safely off the road. At this stage the fire is out but is still smouldering," the agency said.

There was a foul smell in the fire's aftermath, the NZTA said.

"If you are travelling by bicycle, scooter or motorbike be aware that there is a putrid smell in the area and you may wish to avoid it, if possible."

The agency said drivers would be diverted at the Paremata roundabout onto Papakowhai Rd, which eventually emerged at Whitford Brown Ave and back onto SH1.

Travellers could also use SH58 or SH2 to reach the city.An enormous clean-up operation was in the works.

"There will be dump trucks, a digger, an all-terrain fork lift and a sweeper truck on the site of the fire from 10am. Extra precautions are being taken as there is believed to be a range of flammable goods on board the truck including paint thinner, batteries and aerosols."

Firefighters were still at the scene of the fire more than three hours after the blaze broke out.

Fire Service shift commander Murray Dunbar said 20 firefighters worked to put the fire out earlier this morning and firefighters were still at the scene beside State Highway 1 at 9.30am dampening down embers. It was not yet clear how long they'd remain there for.

"It just depends on how long they take to take the load out and extinguish it and dispose of it and then tow the truck away," Mr Dunbar said.

Porirua City Council told people to expect "massive" delays after the fire.

The New Zealand Transport Agency (NZTA) advised people to take the train from Paremata station.