A father who drowned after successfully rescuing his child from the water at Seatoun Wharf couldn't swim, his wife says.

Wellington man Valeliano Mita rushed to his son's rescue in the harbour on Saturday despite not knowing how to swim.

The 40-year-old leapt into the water after his son fell in the water. The boy was rescued by members of the public and Mita was taken to hospital in a critical condition. He died a short time later.

Mita's wife told the Herald she missed her husband, whose tragic act of heroism sparked emergency calls in the capital city's eastern suburbs about 8.35pm on Saturday.

Valeliano Mita, 40, drowned after rescuing his son at Seatoun Wharf.

Mita's son was expected to make a full recovery, a police spokeswoman said.

Mita's death will be referred to the Coroner.

Residents around Marine Parade described several ambulances, police cars and a fire truck blocking off the street as ambulance staff performed CPR for a lengthy period of time on Saturday night.

A small crowd of onlookers had gathered on the wharf during the incident.

One neighbour, who asked not to be named, said a child could be seen wrapped in a towel at the scene.

Mark Cleverley, who lives a few doors down from the wharf, said he first noticed a gathering of emergency services as the sun set.

Once two ambulances arrived he knew something terrible had happened, he said.

But swimming around the Seatoun Wharf was generally considered safe by locals, Cleverley said.

"What happens is the youngsters jump off the wharf all the time. There might have been a bit of jumping there and someone's hurt themselves," he said.

"It was pretty full-on down there with all the cops."

Cleverley said there had been some of the usual Wellington winds blowing.

"It's pretty open there."

Several other residents described the sea as typically choppy and wild, and said the beach had been quiet throughout the day.

"I'd be surprised if anyone had gone swimming out there," one said.

Senior lifeguard Jonathon Webber, who is an advisory board member for Drowning Prevention Auckland, said the incident was "a real tragedy" and highlights the phenomenon of "aquatic victim instead of rescuer syndrome".

He said such scenarios, where someone dies trying to help another person, result in about 2 per cent of fatal drownings.

"Typically the person in trouble survives and the would-be rescuer fatally drowns."

Those who notice someone in trouble in the water, Drowning Prevention Auckland advises, should first check for danger before attempting to provide the person with flotation and calling 111.

Rescuing from land or a craft is safest. If entering the water try to take something that floats with you.