Mr Hubbard, 83, and wife Jean, 82, were rushed to Dunedin Hospital yesterday afternoon after their car and a ute collided on State Highway 1 in Richmond, about 5km north of Oamaru around 1pm.
Mr Hubbard died on the way to hospital.
Tributes are appeared on two Facebook supporters websites.
Website creator John Funnell says Mr Hubbard was generous and helped many people.
"He was so trusting of people, he went out of his way to help people and lived a very careful lifestyle,'' says Mr Funnell.
Posts on the Help Allan Hubbard Facebook page have spoken of Hubbard's integrity and generosity.
Amy Parkinson said it was "a NZ tragedy for a man that only ever helped" and Tim Scott said the country would "never forget the good Mr Hubbard did", while Beth McPherson said he was a "great person with old fashioned values where his word was his bond" who did so much for South Canterbury.
Similar sentiments were shared on the Leave Allan Hubbard alone page, with many giving their deepest sympathies to Mr Hubbard's family.
Late last night authorities refused to give any details of the Hubbards' conditions, saying the family had requested privacy.
The couple's daughter, Lesley Limbe, travelled from her Geraldine home to be with her parents.
The driver of the ute suffered minor injuries.
One witness said the crash happened on a straight and usually safe stretch of road.
Supporters of Mr and Mrs Hubbard said the accident was terrible for the couple, who have huge support despite facing serious fraud charges.
"Absolute dismay that this has happened," said John Funnell of the Leave Allan Hubbard Alone supporters' group before it was revealed that Mr Hubbard had died.
"When they should be sitting back, relaxing and enjoying life, they've got 50-odd charges against them in court and now they are both in hospital in serious condition."
Other supporters registered shock on the group's Facebook site last night.
South Island St John Ambulance spokesman Ian Henderson said all three people involved in the crash were originally taken to Oamaru Hospital.
The driver and sole occupant of the ute, Andy Earl, 40, of Nelson was discharged with cuts and abrasions.
Mrs Hubbard was then taken by ambulance to Dunedin Hospital but her husband was airlifted.
Mrs Hubbard, who was driving, had fracture injuries.
Mr Hubbard had multiple injuries, including to his legs.
Carole Perry, who lives just south of where the accident happened, was driving north when she came across the scene.
Police, fire and ambulance services were at the scene, tending to the injured, and traffic was backed up.
"From where we were, I could only see the back end of the little white car, which didn't look good.
"It's a perfectly straight piece of road so I don't know what's happened," she said.
Yesterday's crash came just over a year after the collapse of South Canterbury Finance, the business Mr Hubbard developed into what was once New Zealand's largest finance company.
The collapse came after the Government's decision in June last year to place Mr Hubbard and his business interests under statutory management during a Serious Fraud Office investigation.
South Canterbury's receivership on August 31 last year triggered a record bailout under the Government's deposit guarantee scheme, giving $1.7 billion of taxpayers' money to 35,000 investors.
The statutory management decision triggered outpourings of support including street rallies for Mr Hubbard, who lived in Timaru.
Much of that support persisted after the Serious Fraud Office charged him in June with 50 counts of fraud and related offences.
The office alleged that some of his clients believed they had investments with him of more than $1 million, but that these did not exist.
Mr Hubbard was to have appeared in Timaru District Court next month.
