Zuckerberg pledge beats Buffett challenge

Mark Zuckerberg's pledge to give away his Facebook holdings is the latest philanthropic initiative by America's wealthy, and follows a challenge by billionaire Warren Buffett to the world's other billionaires.

The announcement by the Facebook founder and his wife Priscilla Chan to donate 99 per cent of their Facebook shares, or some $US45 billion ($A61.4 billion), to charitable causes during their lifetime far exceeds the challenge by Buffett, who urged the wealthy to give away at least half their fortunes.

The "Giving Pledge" was launched in 2010 by Buffett and Microsoft co-founder Bill Gates, who have been among the world's richest individuals over the past decade.

The two business icons had called on the wealthy to pledge to charity at least half their assets during their lifetimes or upon their deaths.

They quickly enlisted a small group that included CNN founder Ted Turner, then-New York mayor Michael Bloomberg, Oracle co-founder Larry Ellison and Hollywood director George Lucas.

In the group's latest update in June, the list had grown to 137 individuals and families.

Those who signed the pledge come from 14 countries: Australia, Brazil, Germany, India, Indonesia, Malaysia, Russia, South Africa, Taiwan, Turkey, Ukraine, United Arab Emirates, Britain and United States.

"When we started the Giving Pledge five years ago, we had no idea we'd get this many people to come together. It has really grown, first in the US but more recently all over the world," said Gates in a statement.

"We hope to intensify philanthropy and encourage people to get started younger. It's exciting to see people becoming bolder and more thoughtful in their giving. This is about building on a wonderful tradition of philanthropy that will ultimately help the world become a much better place."

While the giving initiative has gained momentum, especially among tech billionaires, the tradition of philanthropy has a long history in the United States.

A group of wealthy industrialists who made fortunes in the late 19th and early 20th century - denigrated by some as "robber barons" - became known for their philanthropy as well.

These included Andrew Carnegie, John D. Rockefeller, Cornelius Vanderbilt and Henry Ford.