Barack Obama has revealed he is shocked at how wealthy he has become after the presidency in a speech calling for higher taxes on the rich.

Speaking in South Africa on Tuesday, the former president said he'd happily sacrifice a little of his wealth to help the needy, joking that there are 'only so many nice trips you can take.'

'Right now I'm actually surprised by how much money I got,' he told an audience of 10,000 at the event to at to honor Nelson Mandela, in Johannesburg. 'And let me tell you something — I don't have half as much as most of these folks, or a tenth, or a hundredth,' he said, before saying that it was enough, The Hill reports.

Barack Obama has revealed he is shocked at how wealthy he has become after the presidency in a speech in Johannesburg calling for higher taxes on the rich

'There's only so much you can eat,' he said, smiling. 'There's only so big a house you can have.

'There's only so many nice trips you can take,' he added, perhaps a reference to the fact that Barack and Michelle spent months on back-to-back vacations kite-surfing in the British Virgin Islands, yachting with celebs around French Polynesia and relaxing in Tuscany, Italy after leaving office last year.

While her husband is in South Africa, Michelle spent Sunday dancing the night away in Paris, the front row of a Beyonce concert, with the singer's mother Tina Knowles Lawson, right beside her and reportedly her daughter Sasha in the crowd.

Barack Obama has an estimated net worth of $40 million, according to CelebrityNetWorth.com, much of it from book deals and speaking appearances.

But his real worth is likley to be much higher with him frequently accepting six-figure speaking appearances, including a $400,000 gig from Wall Street. Barack and Michelle also signed book deals with Penguin Random House worth a combined $65 million for their respective memoirs.

In May this year they signed a deal with Netflix to produce series and movies for the streaming service. While the financial details of the deal have been kept a closely guarded secret, it is likley to match Grey’s Anatomy creator Shonda Rhimes' contract worth more than $100 million.

Barack said he would happily share some of that wealth to support families struggling at the other end of the spectrum.

'I mean, it's enough. You don't have to take a vow of poverty just to say, 'Let me help out a few of the other folks,' he said, to applause.

Speaking in South Africa on Tuesday, the former president said he'd happily sacrifice a little of his wealth to help the needy, joking that there are 'only so many nice trips you can take' (Obama kitesurfs at Richard Branson's Necker Island retreat on January 29, 2017 in the British Virgin Islands)

Barack and Michelle spent months on back-to-back vacations, such as yachting with celebs around French Polynesia (pictured)

'Let me look at that child out there who doesn't have enough to eat or needs some school fees — let me help them out.

'I'll pay a little more in taxes,' Obama continued. 'It's OK, I can afford it. I mean, it shows a poverty of ambition to just want to take more, and more, and more, instead of saying, 'Wow, I've got so much, who can I help? How can I give, more, and more, and more?''

Obama was speaking months after Donald Trump came under fire for his tax reform which cut taxes for the rich and corporations, and reduced deductions for the middle class.

It included plans to eliminate the federal estate tax, a levy paid only by estates worth more than $5.5 million for individuals and $11 million for couple, and to scrap the alternative minimum tax, a supplemental tax which only effects households who earn more than $200,000.

It also dropped corporate tax rates to just 20 per cent, benefiting wealthy business owners, and axed tax deductions for many middle class Americans such as student loan interest deduction and state and local tax deduction.

'There's only so big a house you can have,' he added (the Obamas' Washington DC house in the upmarket Kalorama neighbourhood)

He also told the crowd on Tuesday that 'There's only so much you can eat,' before it was time to share the wealth

The legislation was generally unpopular but passed, giving Republicans, who promised tax reform in the election, a win.

When Trump first floated the plan during his campaign, Obama had criticized it, saying it would only 'help people like him.'

In a speech on the economy in Indiana in June, 2016, he said: 'That will not bring jobs back,' Obama said.'That is not fighting for the American middle class. That will not help us win. That is not going to make your lives better. That will help people like him.'

In contrast, President Obama's administration implemented a small raise on taxes, mostly to help pay for Obamacare, and put a bigger focus on using tax policy to readdress wealth distribution.

But there no significant raises, despite claims from the Republicans that Obama was responsible for hikes, and president number 44 had even signed a compromise bill making permanent the tax cuts enacted by George W. Bush.

Big appearance: Obama was front and center as he marked 100 years since the birth of Nelson Mandela

Making moves: Obama danced with singer Thandiswa Mazwai who performed after his speech, with Mandela's widow Graca Machel and South African president Cyril Ramaphosa also taking part

Meanwhile, on Tuesday, Obama also took aim at 'strongman politics' in his highest-profile speech since leaving office, urging people around the world to respect human rights and other values now under threat in the address marking the 100th anniversary of anti-apartheid leader Mandela's birth.

Obama's speech in South Africa countered many of Trump's policies, rallying people to keep alive the ideas that Mandela worked for including democracy, diversity and tolerance.

Obama spoke to a crowd of more than 10,000 people at a cricket stadium in Johannesburg in the centerpiece event of celebrations marking 100 years since Nelson Mandela's birth.

Obama opened by calling today's times 'strange and uncertain,' adding that 'each day's news cycle is bringing more head-spinning and disturbing headlines.' These days 'we see much of the world threatening to return to a more dangerous, more brutal, way of doing business,' he said.

He targeted politicians pushing 'politics of fear, resentment, retrenchment,' saying they are on the move 'at a pace unimaginable just a few years ago.'

Obama added: 'I am not being alarmist, I am simply stating the facts. Look around.' He also spoke up for equality in all forms, saying that 'I would have thought we had figured that out by now.'

Address: Graca Machel, Nelson Mandela's widow, spoke before Obama at the Wanderers Stadium in Johannesburg, South Africa, marking 100 years since his birth

And he warned: 'Social media, once seen as a mechanism to promote knowledge, has proved to be just as effective promoting hatred and paranoia and conspiracy theories.'

He also spoke up more than once for the 'free press' saying it was 'under attack' and needed to be defended - in contrast to Trump calling the media 'the enemy of the people'.

'Democracy depends on strong institutions,' he said.

'It's about minority rights, and checks and balances and freedom of speech, free press, and the right to protest and petition the government, and an independent judiciary, and everybody having to follow the law.'

And the former president spoke about the 'utter loss of shame among political leaders when they're caught in a lie and they just double down and lie some more'.

'People just make stuff up!' he said to laughter an applause from the audience.

This is Obama's first visit to Africa since leaving office in early 2017. He stopped earlier this week in Kenya, where he visited the rural birthplace of his late father.

Obama's speech highlighted how the Nobel Peace Prize winner, who was imprisoned for 27 years, kept up his campaign against what appeared to be insurmountable odds to end apartheid, South Africa's harsh system of white minority rule.

Mandela, who was released from prison in 1990 and became South Africa's first black president four years later, died in 2013, leaving a powerful legacy of reconciliation and diversity along with a resistance to inequality, economic and otherwise.