UPDATED 1.13pm: Police divers at Hunua Falls south of Auckland have found the body of a young man who went underwater and did not resurface.

He was one of a group swimming at the popular falls last night, when he got into trouble.

One of his friends and two other swimmers tried to reach the man, but he slipped under the water and did not come up by the time it got dark.

One of the would-be rescuers was taken to hospital by the Westpac Helicopter in a moderate condition, and is not on the mend.

Police were at the scene overnight and the Wellington-based police dive squad arrived this morning.

Senior sergeant Jono Chappell said the scene was guarded overnight.