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Motorists stuck in long queues of traffic on the new motorway extension north of Auckland are advising other drivers to stay away.

The $365 million Northern Gateway toll road opened at 2am this morning and while some of those stuck in traffic are simply trying to get up north, others are making the most of the road being free until Tuesday and driving up for a look.

"Traffic is heavy coming through the tunnel and motorists who do wish to travel on the toll road should expect a 30 minute delay to their journey," the New Zealand Transport Agency (NZTA) reported late this morning.

"It's great that people are taking the opportunity to get used to the toll road, but they should remember that they are travelling on a motorway and need to take care not to hold up traffic following behind," NZTA traffic management unit manager Mark Walker said.

Brad Collett is trapped in a car near Hatfield's Beach on a sightseeing trip which has turned into a traffic nightmare. He says it seems half of Auckland had the same idea.

Mr Collett says times are tough so people are clearly trying to find free entertainment where they can.

Mr Walker suggests anyone going further north than Puhoi should take the alternative route via State Highway 16.

"The existing free route via Orewa can also be used. Motorists should look out for on-road electronic signs to direct them to SH16 and listen to the radio for traffic updates," he said.

The toll charges of $2 for cars and $4 for trucks will come into effect at midnight tomorrow, the end of Auckland Anniversary weekend.