At one point in the early afternoon in New York, the Nasdaq composite index - which reflects the value of tech firms - was down nearly 7% on the day, and had plunged to just half its value from from the high point of 5, 048.6 it reached on 10 March.

BBC: Tech shares battered on Wall Street

An exception was the Shanghai Composite index, which ended the day 1.8% higher, largely due to a surge in the value of energy companies, including a 10% jump in China Shenhua Energy Company.

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