India's Mukesh Ambani has lost his crown as Asia's richest person after the latest rout across global markets wiped almost six billion U.S. dollars off his fortune, according to the Bloomberg Billionaires Index.

All told, the world's 500 richest people lost 238.5 billion U.S. dollars on Monday, according to Bloomberg, the biggest daily plunge since the index began tracking them in October 2016.

Equity and oil markets went into meltdown on what has been dubbed Black Monday as growing fears about the economic impact of COVID-19 were compounded by Saudi Arabia's decision to slash crude prices following a row with Russia over production cuts.

Crude prices tanked by a third in their worst drop since the 1991 Gulf War.

The sell-off erased 5.8 billion U.S. dollars from 62-year-old Ambani's net worth to leave him with a net worth of about 41.8 billion U.S. dollars.

He was overtaken by Chinese tycoon Jack Ma, founder of Alibaba whose fortune had fallen about 1.1 billion U.S. dollars to 44.5 billion U.S. dollars. Ma, 55, had ceded the number-one ranking in mid-2018.

The slump in oil prices raises questions about plans by Ambani's Reliance conglomerate to cut debt as they hinge on selling a stake in its oil and petrochemicals unit to Saudi Aramco, Bloomberg reported.

Ambani, whose fortune ballooned on the back of India's telecoms boom, lives with his family in a 27-story luxury Mumbai skyscraper reputed to have cost more than one billion U.S. dollars to build.

The carnage on global markets on Monday also lost Amazon founder and world's richest man Jeff Bezos 5.6 billion U.S. dollars and Berkshire Hathaway's Warren Buffett 5.3 billion U.S. dollars, Bloomberg said. However, they still have fortunes of 111.8 billion U.S. dollars and 76.4 billion U.S. dollars respectively.

Frenchman Bernard Arnault, chairman of luxury-goods giant LVMH, was Europe's biggest decliner with a 4.4-billion-U.S.-dollar drop in his net worth to 81.4 billion U.S. dollars.