Two motorcyclists are dead after two separate crashes in the North Island.

A motorcycle pillion passenger is dead and two other people injured after a crash involving two motorcycles and a car near the Kaipara Harbour northwest of Auckland.

And another motorcyclist is dead after an unrelated crash involving a four-wheel-drive and a motorcycle on Russel Rd in Whangarei.

The Kaipara crash occurred on State Highway 16 near Ogle Rd at around 2.50pm.

Advertisement

One motorcycle rider was seriously injured and transported to Auckland Hospital by helicopter and the driver of the car was moderately injured and transported by ambulance to North Shore Hospital.

Ambulance and the Westpac Auckland rescue helicopter responded to the crash.

An Auckland Rescue Helicopter Trust spokesman said a crew attended the crash at 2.50pm.

"[The] crew assisted one male patient in his fifties, the solo rider of the second bike who dropped his bike and slid under the metal barrier.

"He suffered multiple injuries and was flown to Auckland City Hospital in a serious condition."

NZTA reports the road has been closed, and urges motorists to please avoid SH16 if possible.

Cordons have been placed on roads and the Serious Crash Unit has been notified.

NZTA has advised SH16 is closed between West Coast Road and SH1 due to a serious crash.

They advised to allow extra time and use an alternative route.

This follows another serious crash involving a motorcycle on Sunday night in Auckland.

One person was critically injured and another seriously injured in that incident after a motorcycle and car crashed on Jervois Rd in Ponsonby, Auckland.

Both of the people injured were on the motorcycle, police said.

The serious crash unit attended the scene and diversions were put in place.