Clarke was not the only Australian cricketer to react to the news.
Rodney Hogg said it was "blatant cheating" and said Smith would have to quit as captain.
Discussing the incident on SuperSport before Smith's admission, Shane Warne said: "I don't care who you are you can't tamper with the ball.
"I know the Australian sides I played in never did anything like that.
"I feel a bit for Cameron Bancroft because I don't think he's taken it upon himself to do something and put it in his pocket."
Allan Border said on the SuperSport commentary, "this is a bad look for Australian cricket".
"Certainly, it will go all the way through to Cricket Australia. The directors will get involved. It's that serious," the former Australian captain said.
Brad Hogg, who retired from international cricket in 2008, said it was "out of character" for Bancroft.
Former Australia batsman Jimmy Maher called it "a national day of shame" for the country "and for the entire cricket world, really."
Former Australia wicketkeeper Adam Gilchrist said he was "stunned", "shocked" and "embarrassed".
Gilchrist told BBC Radio 5 Live: "Stunned and shocked are two words that come to mind and then when you learn more about it I feel embarrassed and sad.
"It's not what should happen. It should not happen. That's the disappointing thing, it's not (a) spur-of-the moment decision. It's not an under-pressure decision where you make a decision and, 'It's okay I got it wrong because of a pressure moment'. It's pre-planned and premeditated. It's just not acceptable."
Australian media
The Northern Territory News front page was particularly colourful, calling it "cricket's darkest day" and adding "heads are expected to roll".
The news dominated the homepage of The Sydney Morning Herald, with someone on Twitter noting the all-black background: "This must be serious".
Comparing the incident to Richard Nixon's Watergate scandal, Chris Barrett wrote that "it can be the cover-up as much as the crime that brings you down".
"Whatever the label, this is a shameful chapter in Australian cricket and there must be consequences."
He was one of a number journalists saying it was the biggest scandal to hit an Australian cricket captain since Greg Chappell told his brother Trevor to bowl underarm against New Zealand in 1981.
"What took place at the foot of Table Mountain was dumb and deplorable in equal measure," Barrett wrote, concluding that "it will be something the Australian team has to live with for a long time".
Patrick Smith, a columnist for The Australian, said Australian cricket "needs a clean out".
"That Steve Smith has not already stepped down as skipper indicates he still does not know the gravity of his actions. Something awful was always going to be the result of the Aussies continually moving 'the line'," he wrote on Twitter.
ABC cricket commentator Catherine McGregor said Smith's position was now untenable.
"One it is culpably stupid but, secondly, it's just an appalling and deliberate systematic attempt to undermine the rules and laws of the game.
"I think the captain's position's untenable. There's no euphemism left for this, this is cheating."
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Peter FitzSimons, a journalist and former rugby union player, called it "cold-blooded, premeditated, clear-eyed CHEATING".
Calling for Smith to be resign or be sacked, he wrote: "As a nation, our name has been slurred, and as a nation, we must be seen to react."
Broadcaster Glenn Mitchell compared the incident to Mike Atherton's ball-tampering in 1994.
Australian politicians
Politicians were quick to weigh in on the scandal, too.
Australian Prime Minister Malcolm Turnbull branded the actions of Smith and Bancroft "completely beyond belief" and "a shocking disappointment" and called for Cricket Australia to take "decisive action soon".
"We all woke up this morning shocked and bitterly disappointed by the news from South Africa," Turnbull told reporters in Australia.
"It seemed completely beyond belief that the Australian cricket team had been involved in cheating. After all, our cricketers are role models and cricket is synonymous with fair play.
"How can our team be engaged in treating (cricket) like this? It beggars belief.
"Let me tell you what has happened today from my point of view. I have spoken with David Peever, the chairman of Cricket Australia a few moments ago, and I have expressed to him very clearly and unequivocally my disappointment and my concern about the events in South Africa and he has said to me that Cricket Australia will be responding decisively, as they should.
"It's their responsibility to deal with it, but I have to say that the whole nation, who holds those who wear the baggy green up on a pedestal - about as high as you can get in Australia, certainly higher than any politician, that's for sure - this is a shocking disappointment. It's wrong and I look forward to Cricket Australia taking decisive action soon.
"I think I speak for all Australians in saying how shocked and disappointed we all are. It honestly seems beyond belief. And I have to say, knowing a number of the players, including the captain, quite out of character. But it's been admitted."
Bill Shorten, the Labor leader, also called on Cricket Australia to act speedily.
Richard M Colbeck, Liberal Senator for Tasmania, said he was "bloody furious".
Senator David Leyonhjelm compared the issue to politicians who "fiddle with expenses".
"Just imagine if it was a politician fiddling with their expenses, everyone would be howling for them to resign," he told ABC News.
"It seems to me that this might be somewhat similar."
Social media
On Twitter, there were those who complained about how it set a bad example for the children.
Others said Bancroft should have refused.
And of course there were the memes, with celebrity chef Adam Liaw referring to a recent row in which Australian Home Affairs Minister Peter Dutton announced plans to resettle "persecuted" white South African farmers.
The backlash in Britain
The Daily Telegraph
Former England captain Michael Vaughan called it "utterly brainless" and said this would "stay with Smith forever".
"This stain on his reputation will not go away," he wrote in The Telegraph.
The Times
Independent
Cricketing world
BBC commentator Jonathan Agnew said Smith's position as captain was untenable.
And former cricketer Kevin Pieterson suggested coach Darren Lehmann knew what was going on.
Pietersen then added that neither Smith, Lehmann nor bowling coach David Saker could continue in their roles, saying they had "disgraced" their country and the game.
The former England batsman wrote on Twitter: "Slept on it...Lehmann, Saker & the leaderships groups jobs are untenable! "They've disgraced a great cricketing nation & Test cricket!"
