Bill Gates pledged on Thursday to give away almost his entire personal wealth in the next two decades and said the world's poorest would receive some $200-billion via his foundation at a time when governments worldwide are slashing international aid.

He also hit out at Elon Musk, the world's richest man and a key figure in President Donald Trump's administration, accusing him of "killing the world's poorest children" with huge cuts to the United States aid budget.

"The picture of the world's richest man killing the world’s poorest children is not a pretty one,” Gates told the Financial Times. The Musk-led Department of Government Efficiency has led to the decimation of the US Agency for International Development (USAID), which has previously provided billions in funding for everything from vaccines for children to emergency food assistance.

Gates and Musk once agreed over the role of the wealthy in giving away money, but have since clashed several times.

Gates said he was speeding up plans to divest his fortune and close the Gates Foundation on December 31, 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," the 69-year-old billionaire Microsoft co-founder and philanthropist wrote in a post on his website.

"There are too many urgent problems to solve for me to hold onto resources that could be used to help people."

In an implicit rebuke to Trump's slashing of aid since returning to office in January, Gates' statement said he wanted to help stop newborn babies, children and mothers dying of preventable causes, end diseases like polio, malaria and measles, and reduce poverty.

"It's unclear whether the world’s richest countries will continue to stand up for its poorest people," Gates added, noting cuts from major donors including Britain and France alongside the United States, the world's biggest donor.

Gates said that despite the foundation's deep pockets, progress would not be possible without government support.

He praised the response to aid cuts in Africa, where some governments have reallocated budgets, but said that as an example polio would not be eradicated without US funding.

Gates made the announcement on the foundation's 25th anniversary. He set up the organisation with his then-wife Melinda French Gates in 2000, and they were later joined by investor Warren Buffett.

"I have come a long way since I was just a kid starting a software company with my friend from middle school," he said.

FOUNDATION HAS GIVEN $100BN

Since inception, the foundation has given away $100-billion, helping to save millions of lives and backing initiatives like the vaccine group Gavi and the Global Fund to Fight AIDS, Tuberculosis and Malaria.

It will close after it spends around 99% of his personal fortune, Gates said. The founders originally expected the foundation to wrap up in the decades after their deaths.

Gates, who is valued at around $108 billion today, expects the foundation to spend around $200-billion by 2045, with the final figure dependent on markets and inflation.

The foundation is already a huge player in global health, with an annual budget that will reach $9-billion by 2026.

It has faced criticism for its outsize power and influence in the field without the requisite accountability, including at the World Health Organization.

Gates himself was also subject to conspiracy theories, particularly during the Covid-19 pandemic.

Gates has spoken to Trump several times in recent months on the importance of continued investment in global health.

"I hope other wealthy people consider how much they can accelerate progress for the world’s poorest if they increased the pace and scale of their giving, because it is such a profoundly impactful way to give back to society," Gates wrote.