A man who drowned at Whangamatā was swimming in a estuary when he was swept out to sea on an outgoing tide.

Lifeguards are warning swimmers to be cautious in estuaries after the incident.

An elderly man swimming with a friend in the estuary at Whangamatā beach died on January 17.

The area, near the mouth of the Otahu river, is often popular with families and kayakers as it is perceived to be a safer, flatter area than the main surf beach, but people can still be swept out to sea, says Surf Life Saving NZ Eastern regional manager Chaz Gibbons-Campbell.

The man got into difficulty when the tide swept him from the estuary into the ocean, says Chaz.

"There was a group at the estuary at the south end of Whangamatā beach. A couple were swimming in the estuary and an older gentleman was swept out into the sea."

Chaz says people should be aware that this can happen in areas of water people may perceive to be safe.

"The estuary is still tidal and so it can happen quickly that a swimmer could be swept into the wider ocean. There had been a high tide at 4pm so there was a large swell in the estuary and lots of water.”

Police contacted lifeguards just after 6pm.

'The patrol lifeguards finish at 6pm but fortunately there were some still around and they quickly went to the scene a few minutes after the alert.They were then joined by lifeguards from other areas. The man was located with the help of the Westpac helicopter and lifeguards brought him to shore around 7pm, but after all efforts he was sadly unable to be revived."

Chaz says thoughts are with the man's family and those who had been at the beach.

The north side of Whangamatā beach is patrolled by surf lifesaving through the season until April, while the south side is only patrolled with additional lifeguards during the busy holiday season from December 26 until January 13.

"Our key safety messages, as always, are for people to swim between the flags and to be aware of your swimming capabilities and how conditions can quickly change."

Additional lifeguards were on duty at the beach on January 18, and are supporting those involved in the incident.

Stephanie Peacock Murphy was at the beach with her sons, 9 and 11, walking the family dog, and witnessed the man being found and brought back to shore.

"We actually thought it was a drill to begin with, and it was very impressive to see the skills of all members of Surf Life Saving and the rescue helicopter - highly commend them all. Lots of sensitive questions were answered to my children on our solemn walk home after witnessing this sad loss of life. We are thinking of his family and loved ones at this time."

The death has been referred to the coroner, says police.