Microsoft founder Bill Gates has said he intends to give away 99% of his vast fortune over the next 20 years.

Gates said he would accelerate his giving via his foundation, with plans to end its operations in 2045.

"People will say a lot of things about me when I die, but I am determined that 'he died rich' will not be one of them," he wrote in a blog post on Thursday.

Mr Gates, 69, said his eponymous foundation has already given $100bn (£75bn) towards health and development projects, and that he expects it will spend another $200bn, depending on markets and inflation, over the next two decades.

In his blog post, Mr Gates cited a 1889 essay by tycoon Andrew Carnegie called The Gospel of Wealth, which argues that wealthy people have a duty to return their fortunes to society.

Mr Gates quoted Mr Carnegie, who wrote: "The man who dies thus rich dies disgraced."

His latest pledge represents an acceleration in charitable giving. Initially, he and his ex-wife Melinda had planned for the Gates Foundation to continue working for several decades after their deaths.

When asked about this shift, Mr Gates told the BBC's Newshour on Thursday that there will be other wealthy people in 20 years who can better tackle future challenges.

"It's really about the urgency," he said. "We can spend a lot more if we're not trying to be perpetual, and I know that the spending will be in line with my values."

Giving away 99% of his fortune could still leave Mr Gates a billionaire – according to Bloomberg, the Microsoft founder is the fifth-richest person in the world.

In the blog post, he shared a timeline of his wealth that showed his current net worth at $108bn and a large hand-drawn arrow going down to close to zero in 2045.

Mr Gates also said the foundation would draw from its endowment to give away $200bn.

Along with Paul Allen, Mr Gates founded Microsoft in 1975, and the company became a dominant force in computer software and other tech industries. Mr Gates has gradually stepped back from the company this century, resigning as chief executive in 2000 and as chairman in 2014.

He said he has been inspired to give away money by investor Warren Buffett and other philanthropists, however critics of his foundation say Mr Gates uses its charitable status to avoid tax and that it has undue influence over the global health system.

In his blog post, he outlined three main goals for his foundation: eliminating preventable diseases which kill mothers and children; eliminating infectious diseases including malaria and measles; and eliminating poverty for hundreds of millions of people.

Mr Gates criticised the US, UK and France for cutting their foreign aid budgets.

"It's unclear whether the world's richest countries will continue to stand up for its poorest people," he wrote. "But the one thing we can guarantee is that, in all of our work, the Gates Foundation will support efforts to help people and countries pull themselves out of poverty."

He was more pointed in the interview with Newshour, where he was asked about comments he had made accusing tech billionaire Elon Musk of killing children through cuts to US aid made by Department of Government Efficiency, or Doge.

"These cuts will kill not just children, but millions of children," Mr Gates replied.

"You wouldn't have expected the world's richest person to do it."

In his interview with the BBC's Newshour, Mr Gates raised the issue of cancelled grants to a hospital in Gaza Province, Mozambique, which Donald Trump erroneously claimed was funding condoms "for Hamas" in the Gaza Strip. Mr Musk later acknowledged the claim was wrong and said "we will make mistakes", however the cost-cutting continued.

"I'm disappointed that [Musk] made abrupt cuts and characterised them in a way that was unfair, including saying that, money was being spent in Gaza when in fact, it was money to prevent mothers from infecting their babies with HIV," Mr Gates said.

"I mean, this is serious stuff," he continued.

The BBC has contacted Mr Musk for comment.

The Gates Foundation is a donor to BBC Media Action, the BBC's charitable arm which is separate from the Corporation's news operations.