Billionaires including Amazon's Jeff Bezos and Tesla founder Elon Musk have seen their wealth soar during the COVID-19 pandemic while the world's poor face years of hardship, charity Oxfam said on Monday as it demanded steps to tackle inequality.

Nations have a "shrinking window of opportunity" to build a fair, green recovery, according to "The Inequality Virus" report, published as global leaders tune in for the World Economic Forum's virtual "Davos Dialogue" meeting.

"We stand to witness the greatest rise in inequality since records began," Gabriela Bucher, executive director of Oxfam International, said in a statement as the charity called for higher wealth taxes and stronger protections for workers.