A four wheel drive towing a caravan has collided with a truck on State Highway 1 in Warkworth this morning.

Gas bottles being carried by one of the vehicles have exploded as a result.

The Fire Service said the incident occurred on the Mahurangi River Bridge on Brown Rd.

Police say as a result of the gas bottles exploding, the Fire Service are in attendance and the road has been closed to both north and south bound traffic.

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There are no reported injuries to any persons at this stage and the Fire Service confirmed no one is trapped.

The crash closed one of the major routes north of Auckland but it has now reopened.

State Highway 16 has only just reopened after a multi-vehicle crash in Kumeu, Auckland earlier this morning.

Two people were left in serious condition and four have minor injuries as a result of that crash, which involved three cars.

State Highway 16 near Foster Rd was down to one lane but is now open.

NZTA tweeted about 10am to say State Highway 16 is open near Foster Rd in Waimauku.

The agency said traffic remains heavy across Auckland.

"Please allow plenty of time for your journey and take extreme care."