Three motorbike crashes on the country's roads this weekend have left five people hospitalised.

A woman is undergoing surgery after she crashed into a road barrier in South Auckland just after midday today, police said.

The crash happened at the State Highway 1 and 2 interchange, on the southern side of the Bombay Hills.

A Middlemore Hospital spokeswoman said the woman was in a critical condition after suffering significant injuries.

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She was flown to Middlemore Hospital by the Westpac Rescue Helicopter.

Initial indications were that neither speed nor alcohol were factors in the crash, police said.

Also today, a Marlborough man was flown by the Nelson Marlborough Rescue helicopter to Nelson Hospital after a crash in the Wairau Valley.

The Blenheim man, in his 50s, was riding his motorbike with friends along SH63 near Tophouse when an animal ran across the road, causing him to lose control and fall from his bike, a rescue helicopter spokesperson said.

He was treated at the scene for leg injuries.

Yesterday, three motorbikes and a truck collided on Auckland's Harbour Bridge about 12pm, leaving two motorcyclists with critical injuries and a third with serious injuries.

Three northbound lanes were closed while emergency services attended the scene of the crash.

Meanwhile, a woman in her 40s was flown by the Taupo-based Greenlea Rescue Helicopter to Hastings hospital with hip and back injuries following a vehicle crash this afternoon.

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The incident happened in the Waipunga Gorge on SH5, southeast of Taupo, a rescue helicopter spokesman said.