Police are investigating a serious assault at Paremoremo, north of Auckland, this morning.

One man has been flown to Auckland Hospital with serious head injuries, while another has been taken to Middlemore Hospital by ambulance with moderate injuries to his hand.

The people were found in the mudflats near Lucas Creek after the incident about 8am.

Senior Sergeant Shanan Gray said the woman was also taken to hospital as a precaution.

He said police had not yet spoken to the trio.

Asked if a weapon was involved in the assault, Mr Gray said it was unclear at this stage.

He said no decision had yet been made on what charges would be laid.

The incident occurred near Paremoremo prison.