A motorcyclist has died after colliding into the back of a traffic attenuator truck, moments after Police spotted them speeding on Auckland's Southern Motorway last night

A Police motorways unit signalled the motorbike to stop after 11pm near Otara, however the driver continued so it didn't pursue.

A short time later, the officers were travelling south when a truck driver flagged them down because the motorbike collided into the rear of his vehicle by the East Tamaki Road off-ramp.

Police say the male rider sustained fatal injuries and died at the scene.

An investigation is now underway into the crash and the Independent Police Conduct Authority has been notified.