A search is underway for a swimmer missing in the Waikato River.

The report of a missing swimmer was received by emergency services shortly after 6pm.

Initial reports indicate a group of four people had gone into the water but only three have come back to shore, says a statement from Police.

After receiving the report the Westpac Rescue Helicopter was immediately deployed to search by air however that search was unsuccessful, says the statement.

'Searchers are continuing their efforts by boat and jet ski.”

They are searching down river towards Claudelands Bridge and the search will continue until dark, says the statement.