A couple say they encountered waves the size of buildings, winds they couldn't stand in and "whiteness everywhere" as they awaited rescue on their broken yacht off the coast of Sydney, Australia.

Irishman Nick Dwyer and Frenchwoman Barbara Heftman arrived safely in Balmain on Wednesday night aboard a NSW Police rescue vessel with the "absolute heroes" who travelled more than 200 nautical miles in treacherous seas to save them.

"We owe them our lives," Dwyer said.

The experienced sailors had been sailing from New Zealand to Australia in a 12-metre vessel as part of a 10-year circumnavigation of the globe when the yacht's rudder broke on Saturday.

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They activated the yacht's emergency radio beacon three days later, on Tuesday afternoon, after their yacht "rolled" during a heavy swell and high winds.

"Barbara and I were waiting after the boat turned upside down, holding each other, thinking for a split second that seemed to last for an eternity, 'is she going to turn upright?"' Dwyer told reporters in Sydney.

Each time another wave hit, the couple wondered if the sea would ultimately claim their lives.

"We encountered enormous seas, waves the size of buildings coming at you constantly, winds that you can't stand up in and seas breaking, whiteness everywhere," Dwyer said.

The NSW Police offshore patrol vessel Nemesis set off in response to their emergency beacon on Tuesday night and reached the yacht - some 210 nautical miles north-east of Sydney - on Wednesday morning in 6-metre swells and gale-force southerly winds.

"It was truly amazing, to think that somebody had come that far to save us," Dwyer said.

The pair were transferred to the Nemesis by a container ship, the ANL Elanora, while their yacht was left to drift at sea.

Dwyer said the yacht had been their home for the past 10 years and they weren't sure what they would do next.

"Our home's gone, we're alive, I expect to live a little bit longer and that'll be okay," he said.

- AAP