Witnesses to a serious crash between a dirt bike and a four-wheel-drive have been urged to contact police.
One person was critically injured in the Muriwai Beach accident on Sunday afternoon, a police spokesperson said.
"The person riding the dirt bike was critically injured and remains in Auckland Hospital in a critical condition."
Emergency services were alerted to the crash around 3pm.
Police urged anyone who witnessed the incident or was in the area around that time to contact them.
Can you help? Anyone with information should contact Waitemata Crime Squad on 09 839 0697.
You can also call Crimestoppers anonymously on 0800 555 111 or send police a private Facebook message.
• Dirt bike rider dies in South Auckland crash
• Fatal crash: One dead after crash involving two off-road motorbike near Atiamuri
• Dirt bike rider crashes on Whanganui central city footpath after terrifying pedestrians
• Teen injured in dirt bike crash