It's understood that Cairns collapsed, having suffered a massive heart attack last week in Canberra - resulting in an aortic dissection, a tear in the inner layer of the body's main artery.
In a statement today, Melanie Cairns confirmed that her 51-year-old husband has been transferred to a Sydney hospital to undergo further surgery.
"As has now been widely reported in the media, Chris suffered a major medical event in Canberra late last week.
"He initially underwent surgery in Canberra, but the seriousness of his condition is such that he has now been transferred to St Vincent's hospital in Sydney, where he has undergone further cardiovascular surgery," she said.
"Chris' family and friends are heartened by the respectful and warm manner in which this terrible news has been reported, and received by the public, both in New Zealand and around the world, and thanks everyone for their warm wishes, prayers, and kind words.
"For now, no further statements will be made regarding Chris' situation, and the Cairns family asks that people continue to respect their privacy as they deal with this difficult, upsetting and concerning situation."
St Vincent's Hospital in Sydney said Cairns had been admitted on Tuesday after being moved from Canberra for urgent treatment following a serious health event.
"He is in a serious but stable condition in intensive care," a spokesperson said.
New Zealand Cricket chief executive David White said in a statement today: "We're deeply concerned to hear of Chris Cairns' medical emergency. Our thoughts are with his family in Aus and here in NZ. Chris is a much loved husband, father, and son - and remains one of our finest all-rounders.
"We hope he's able to make a full recovery."
Cairns, the son of Black Cap legend Lance Cairns, was a right-hand batsman and fast-medium bowler. He played 62 Tests, 215 one-day internationals and two Twenty20 matches for New Zealand between 1989 and 2006.
Cairns has been living and working in Canberra with Melanie and their children for several years. He has been the chief executive of SmartSportz, a company specialising in virtual sport.
Cairns' mother, Sue Wilson, is in Cairns and unable to get to his bedside in Sydney due to Covid travel restrictions.
The Cairns family has endured personal tragedy. Chris Cairns' sister Louise was killed in 1993 when a cement truck failed to stop at a level crossing at Rolleston in the South Island and collided with the Southerner passenger train.
Cairns had to rebuild his life after walking out of Southwark Crown Court in London in 2015 after being found not guilty of perjury and perverting the course of justice charges in relation to match-fixing allegations.
The news of Cairns's health has rocked New Zealand, where former team-mates expressed sympathy for his family.
"It's absolutely devastating. It's the worst news you could possibly get," former Black Cap Chris Harris told local media.
Cairns has lived in Canberra for several years with his children after his marriage to Australian Melanie Croser in 2010.
After retiring from international cricket, Cairns was the subject of allegations of match-fixing in India as captain of the Chandigarh Lions in the defunct Indian Cricket League (ICL) in 2008.
He denied any wrongdoing and fought several legal battles to clear his name, winning a libel case against former Indian Premier League chairman Lalit Modi in 2012.
In 2015, he was cleared of perjury in relation to the libel case after being charged by Britain's Crown Prosecution Service.
Former New Zealand captain Brendon McCullum, who testified against Cairns during the perjury trial, said the cricket community was suffering along with Cairns's family.
"It's a difficult subject to obviously talk about. We haven't seen each other for quite a long time," McCullum, a host on New Zealand radio station SENZ, said.
"Our relationship is unimportant in the whole thing, the fact is that Chris is a father and also a son to Lance and (mother) Sue.
"Today my family and myself are thinking of those people who are suffering."
- NZ Herald and Reuters
