Shares in London have plummeted in early trading, with the FTSE 100 index of shares plunging 8 percent to its lowest level in three years.
It comes after big falls in Asia, with Japan's Nikkei 225 index down 5 percent while Australia's ASX 200 slumped 7.3 percent, its biggest daily drop since 2008.
Asian investors also reacted to a slump in Chinese export figures and the shrinking of the Japanese economy.
In China, the benchmark Shanghai Composite share index fell 3 percent, while in Hong Kong, the Hang Seng index sank 4.2 percent.
Markets have been rattled by the threat of a price war between oil exporting group Opec and its main ally Russia.
The wobble compounds fears over the effect of coronavirus on the economy.
Oil prices are down more than 20 percent with Brent crude trading at 35 dollars, 98 cents a barrel.
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