A man who was swimming in the Waikato River this afternoon has drowned.

Senior Sergeant Peter van de Wetering said emergency services went to the beach on Malcolm Street in Riverlea, Hamilton, just before 5pm.

The man, thought to have been in his 40s, appears to have been swimming across the river from the city side, and back again.

Senior Sergeant van de Wetering said at some point, he got into a bit of bother, and vanished from the sight of witnesses also swimming in the river.

When he was finally spotted, he was unresponsive.

Paramedics performed CPR but he couldn't be revived.

His identity has yet to be confirmed.