The police national dive squad is on its way to join the search for a man missing in the Waikato River.

Fears are held for the safety of the 21-year-old, who was seen getting in the water near Grantham St in Hamilton just after 3am today.

A witness told police a man was in the water but a police boat failed to find him.

Search and rescue teams scoured the river and riverbank this morning but failed to find the man.