Mr Mundy said anyone who goes swimming should swim between the flags.
“Do not swim alone and stay well within your depth. Be aware that when a large surging wave comes into shore, what was your swimming depth will be lost as the surge carries you out at least an extra metre — that's half the height of an adult.
“If you have been swimming in shoulder-deep water you now are in water well over your head, in a body of water that will want to get back out to sea.”
Mr Mundy said anyone who did get into difficulty should remember the “3Rs” rip survival plan.
“Relax and float to conserve your energy. Raise your hand to signal for help. Ride the rip until it stops and you can swim back to shore or help arrives.”
He said raising your hand will attract attention and indicate that you need help.
“With surf lifeguards doing observational patrols in the area, either we will see you, or someone will alert us to your need.
“Remain calm and continue to float until help arrives.”
The Met Service has warned areas east from Northland to Coromandel, Bay of Plenty to East Cape, Gisborne and down to Hawke's Bay, and maybe even Wairarapa, may be affected by the high seas.
Paid lifeguards remain on duty on week-days through next week at Midway, Waikanae and at Wainui.