Lifeguards managed to rescue all three people but the man died in hospital, the Maritime and Coastguard Agency said.
Two Newquay RNLI lifeboats, Fistral RNLI lifeguards, the Newquay coastguard rescue team, the police, the air ambulance and the ambulance service all attended the scene, local media reported.
“RNLI lifeguards rescued a woman using their jetski and a man and two-year-old child were recovered from the sea by an RNLI lifeboat,” a coastguard spokesman said.
“The child and man were taken to hospital by the coastguard helicopter and the helimed [air ambulance] helicopter. The man, sadly, has since died in hospital.”
Falmouth coastguard said conditions during the rescue were treacherous, with 13ft waves and 10ft breaking waves in the area. According to local radio station Pirate FM, it is thought that the victims were standing on rocks at the beach when they were swept off their feet by a 10-foot wave.
Severe coastal weather has seen thrill-seekers taking photos and filming themselves in treacherous conditions while videos of people getting swept along by waves have gone viral online.
Craig Woolhouse, Environment Agency flood risk manager, said: “We urge people to stay safe on the coast and warn wave-watchers against the unnecessary dangers of taking ‘storm selfies’.”
The rescue came as stormy weather brewed off the west coast of Britain and Ireland, with southwest coasts forecast to see the second-biggest August storm in a decade on Saturday.
The Met Office has issued a yellow weather warning across most of England and Wales, with winds expected to reach 40mph to 50mph inland as a low-pressure system moves in from the west.
Met Office forecaster Mark Wilson said parts of Devon were hit by 55mph winds, and Wales by 58mph winds, in the early hours of Saturday, but that they were expected to be “much, much lighter” on Sunday. No warnings have been issued for Sunday.
Temperatures are expected to drop from a high of 28C (82F) earlier this week to the low 20s (68F) or high teens in many parts this weekend. However, warmer weather should return from the middle of next week before the August bank holiday.
Nicola Maxey, from the Met Office, said autumn had not yet arrived. “There’s certainly some more sunshine around for next week depending on where you are in the country. It’s a low-pressure system passing through, it’s not the end of summer.”
The Bournemouth Air festival, set to take place along the Bournemouth seafront, called off its show after exceptionally high water levels damaged the beach stage areas. “With the more severe storm conditions forecast for today, the decision has been taken to cancel the ticketed Sunsets on the Beach at Boscombe Pier and the evening entertainment on the stage at Bournemouth in the interests of public safety,” a spokesman said.