The world's 62 richest billionaires have as much wealth as the bottom half of the world's population, according to a new report from Oxfam International.

The wealthiest have seen their net worth soar over the five years ending in 2015. Back in 2010, it took 388 mega-rich people to own as much as half the world.

And the Top 1% own more than everyone else combined -- a milestone reached in 2015, a year earlier than Oxfam had predicted.

Oxfam released its annual report ahead of the World Economic Forum in the Swiss city of Davos, a yearly gathering of political and financial leaders. The study draws from the Forbes annual list of billionaires and Credit Suisse's Global Wealth Databook.

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The anti-poverty group, whose leader co-chaired the forum last year, wants to call even more attention to the widening wealth divide. The top 62 saw their net worth rise by more half a trillion dollars between 2010 and 2015, while the 3.6 billion people in the bottom half of the heap lost a trillion dollars.

Each group has $1.76 trillion.

"Wealth is moving rapidly to concentrate at the tippy, tippy top of the pyramid," said Gawain Kripke, the director of policy and research at Oxfam America.

The income gap between the richest and poorest is also growing. The poorest 20% of the world -- who live below the extreme poverty line, living on less than $1.90 a day -- barely saw their incomes budge between 1988 and 2011, while the most prosperous 10% enjoyed a 46% jump.

"The global economy is not working to pull these people out of extreme poverty," said Deborah Hardoon, Oxfam's deputy head of research.

A separate report published last year by the Pew Research Center found that poverty worldwide has fallen by nearly half over the past decade. Still, 71% of the world's population remain low-income or poor, living off $10 or less a day.

As for a global middle class, Pew called it more promise than reality. While the middle class has nearly doubled over the decade to 13% in 2011, it still represents a small fraction of the world's population.

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To help counter inequality, Oxfam is renewing its call for global leaders to crack down on tax havens, where the rich have socked away $7.6 trillion, the group estimates.

Other things Oxfam is advocating: pay workers a living wage and protect workers' right to unionize; end the gender pay gap and promote equal inheritance and land rights for women; minimize the power of big business and lobbyists on governments; shift the tax burden away from labor and consumption and towards wealth and capital gains, and use public spending to tackle inequality.