"The sail boat actually just came across the bow of my boat and I didn't actually see it because there were a lot of yachts around and I was trying to manoeuvre my boat up the harbour - it was literally just one of those accidents."
Yachtsman Mark Shepherd was racing his 40-footer, Origin, in the regatta with three friends when they saw the Antaeus and the 32-foot vintage craft on a collision course.
"We frantically waved and whistled and shouted ... but it was to no avail."
Mr Shepherd said the vintage craft was split it in two. "The man on board must have just seen it out of the corner of his eye and jumped overboard.
"And the poor woman sitting in the [back], she was caught under the bow of the bigger boat ... She was incredibly, incredibly lucky - she could very easily have died."
The timber craft sank in less than a minute and Mr Shepherd sent a mayday to the Coastguard, who arrived within minutes.
Mr St Clair Brown, who was returning home after holidaying north of Auckland, said he threw a life ring to the woman, then pulled her and the man on board.
Antaeus' bow suffered minor damage.
An estimated 9000-10,000 boats were on the harbour yesterday - including competitors in the Auckland Anniversary Day Regatta.
Dietmar Petutschnig and Suzanne Dubose were watching the regatta from their 44-foot catamaran when they heard a mayday call on their radio.
"There was so much traffic in the harbour," said Ms Dubose. "We heard the co-ordinates of the crash and we realised it was close by. By the time the mayday call went out, you could barely see the boat. It was that far under water. It sank so quickly. It was literally in pieces. We could see debris floating on the water.
"The Coastguard did a superb job and got the woman ... back to the base as soon as possible. From crash, to sinking, to rescue would have been 10 minutes."
Ms Dubose said dozens of people watched the rescue from the Hilton hotel, on the end of Princes Wharf, and regatta officials helped pick up debris.
A spokeswoman for the Oceanbridge Anniversary Day Regatta said she didn't see the collision but saw the yacht sink.
"It just went down in seconds - straight down. I've never seen a boat sink so quickly in my whole life."
The Coastguard said volunteers on its ASB Rescue vessel were quickly on the scene and transported the woman in a serious condition to a waiting ambulance at Westhaven Marina.
Spokesman Ray Burge said information about the crash was sketchy but he reminded people of the importance of lifejackets.
"The only thing I can mention is when our Coastguard volunteers turned up to recover the people in the water, they didn't have lifejackets on. I don't know if they had been removed. Hopefully they had lifejackets on. The biggest problem is people take them and don't wear them."
The Harbourmaster's Office said a report was being prepared for Maritime NZ, which was investigating.
