Updated 1.24pm: The death of a 22-year-old man in the Waikato River at Hamilton is being described as a tragic reminder of the river's hidden dangers.

Emergency services searched both sides of the river after the man went missing around nine last night, using thermo-imaging equipment to continue the search after dark.

Further searches were carried out overnight and again at first light.

Police believe the man was not a good swimmer and would have drowned given the river's strong current and snags below the surface.

They say he had attempted to swim the river at a point near Jellicoe Drive.

He is presumed to have drowned after family saw him slip below the surface while another man was attempting to rescue him.