Queues for kilometres north of Auckland

Vehicles are queued for kilometres before the Northern Gateway toll-road tunnel on State Highway 1. Photo / Chris Reed

Two people were seriously injured when a motorcycle lost control and crashed on State Highway 1 north of Auckland this afternoon.

The incident is adding to the mounting traffic chaos for people heading out of the city.

The crash occurred near Perry Rd at Warkworth about 12.20pm, police said in a statement.

Two people were seriously injured, with one being taken to hospital by rescue helicopter.

The road is closed while police investigate the crash, with diversions and electronic signage in place.

Would-be beachgoers aren't the only travellers affected - the Warkworth A&P Show is also on this weekend. Photo / Chris Reed

Vehicles are queued for kilometres before the Northern Gateway toll-road tunnel on SH1.

Would-be beachgoers aren't the only travellers affected -- the Warkworth A&P Show is also on this weekend.

Earlier today, the New Zealand Transport Agency posted on Twitter: "Allow extra time for travel through Warkworth area this weekend with A&P Show on today & Sunday, delays on SH1 are possible."

Traffic was also heavy in Auckland today.

The NZTA's On The Move feature on its website said a crash on the harbour bridge -- which has since been cleared -- was still causing delays southbound.

There was also heavy congestion on the Northern Motorway between Esmonde Rd and Oteha Valley Rd.