One of the sailors — killed in the Sydney to Hobart yacht race after he was fatally struck by sail boom — has been remembered as an experienced veteran of the event.

Nick Smith, a 65-year-old member of the Royal South Australian Yacht Squadron, died on the Bowline during a night of rough weather while undertaking his fifth attempt at the race.

He and Roy Quaden, 55, from Western Australia, were killed when sail booms hit them in the head on different boats.

The men's bodies returned to shore on Friday morning as the famous race suffered its first fatalities in more than 25 years.

Quaden was killed on Flying Fish Arctos while changing one of the sails, which had been "moving violently throughout the night", NSW Police Superintendent Joseph McNulty said.

"It had requested urgent assistance as one of the members was struck in the back of the head by a boom," he told reporters on Friday, referring to a large horizontal pole at the bottom of a vessel's sail.

Quaden could not be revived.

Just hours later, Smith was fatally hit by the Bowline's boom.

The Royal South Australian Yacht Squadron, where the sailor had been a member since 2013, said it would provide counselling to the Bowline crew and other members.

"[Mr Smith] was an experienced crew member, with this being his fifth Sydney to Hobart Race," the squadron said in a statement on Friday.

Both yachts retired from the race — two of the 17 pulled out by 8.45am AEDT on Friday — after a west-southwesterly change brought strong winds to the southern NSW coast and Bass Strait.

The deaths are the first in the race since 1998, when six sailors died in storms, triggering reforms to safety protocols.

The boats have been seized by police who are onboard collecting evidence.

"They're all pretty safe vessels, they go through stringent safety procedures before they proceed to sea," Supt McNulty said.

Supt McNulty warned conditions could worsen overnight as the boats continue towards Tasmania.

"It's going to be a challenging night in the Bass Strait, big seas are coming," he said.

Cruising Yacht Club of Australia Vice Commodore David Jacobs said the deaths would be investigated.

"If there's something that boats can do to try and prevent this happening, we will implement it," he told reporters.

Jacobs said several members of one boat were relatively new to the sport.

"But when you say they're an amateur crew, there are very specific safety requirements," he said.

Jacobs stressed the race would continue and the conditions were not extreme.

"The conditions are challenging, but they're not excessive," he said.

"I am personally surprised that we've lost a number of the super maxis."

NSW Police said the bodies arrived ashore just before 8.30am.

The fatality aboard Flying Fish Arctos occurred about 55km east-southeast of Ulladulla on the NSW south coast late on Thursday night.

Crew members attempted CPR but could not revive their teammate, notifying the Australian Maritime Safety Authority about 11.50pm.

Flying Fish Arctos altered its course to arrive at Jervis Bay on Friday morning.

The crew member aboard Bowline was struck about 55km northeast of Batemans Bay about 2am and fell unconscious, with CPR unsuccessful.

A police vessel escorted the boat to Batemans Bay.

Prime Minister Anthony Albanese paid tribute to the sailors.

"We have sadly awoken to tragedy in the Sydney to Hobart with the awful news two sailors have lost their lives," he said.

"Our thoughts are with the crews, their families and loved ones at this deeply sad time."

NSW Premier Chris Minns also sent his condolences to the men's families.

A sailor thrown overboard during a deadly Sydney to Hobart yacht race was "on his last breath" after being pinned to the side of his boat underwater.

Porco Rosso crew member Luke Watkins ended up in the water around 3.15am today as the 2013 handicap winner passed Green Cape on the NSW coast in strong winds.

"We went down a rather large wave. The boat went into the trough bit the back of the wave in front (which) completely washed the deck," Watkins told ABC news.

"Then we tipped over, what we call a Chinese gybe... and I got pinned to the... side of the boat underwater.

"I somehow managed to unclip myself from the boat as I could feel I was on my last breath.

"When I popped up above the water, the boat was probably 200m in front of me."

Vice-commodore of the Cruising Yacht Club of Australia David Jacobs, which administers the race, said it was believed Watkins was washed 1.2km away from the boat.

Watkins said he activated his emergency position-indicating radio beacon, "cracked" some glowsticks and turned on a head torch he found in his pocket.

After his life jacket automatically inflated, he tried to huddle up and keep warm.

"After about 10 minutes, I could start to feel myself starting to get a bit cold, so I went into to a bit of a survival pose... kept my elbows in," he said.

"It was pretty hard to keep yourself above water a lot of the time.

"I swallowed a fair bit of saltwater. Just tried to keep the thoughts under control."

Watkins was rescued by his Porco Rosso crewmates — an aircraft and four-time line honours champion Master Lock Comanche — which had earlier retired, had been sent to help.

The crew opted to retire at around 4.45am rather than continue into strong-to-gale-force winds in Bass Strait.

Jacobs said the incident would have been "tenfold" times more scary at night.

"Fortunately there are developed systems and procedures to cater for that situation to retrieve the person," he said.

Two competitors were killed on Friday night after they were struck by booms, the large horizontal pole at the bottom of the mainsail, in a separate incidents aboard Flying Fish Arctos and Bowline.

The two yachts have retired from the 628 nautical mile open water race.

"The sailing community is a very close community. There's about a thousand sailors on the water in this race, and to lose two in this fashion is just devastating," Jacobs said.

The deaths were the first in the Sydney to Hobart since the 1998 event, which claimed the lives of six in violent storms and triggered mass reforms to the race's safety procedures.