UK shares have fallen sharply in morning trading, dragging the FTSE 100 index to its lowest level since December 2016.
Both London and major European markets were down more than 2% as a sell-off that started in Asia gathered pace.
Worst-hit sectors included miners, oil companies, carmakers and tech stocks.
Analysts said the arrest of Chinese telecoms giant Huawei’s chief financial officer in Canada had revived worries over US-China trade tensions.
By mid-morning, London’s 100-share index was down 2.6% at 6,744 points, while the Cac-40 in Paris and Frankfurt’s Dax were both 2.4% lower.
Among the biggest fallers in London were mining firms Antofagasta, down 5.8%, and Glencore, which fell 4.9%.
Earlier, Asian markets also sank, with Tokyo’s Nikkei shedding 1.9% and the Hang Seng in Hong Kong falling 2.5%.
“Investors are back in risk-off mode, with markets falling in the UK, mainland Europe and across Asia,” said Russ Mould, investment director at AJ Bell.
“Markets are worried by numerous things: global economic growth, rising interest rates and the US-China trade war.”
Oil prices also dived. Brent Crude was trading almost 5% lower, taking it below $59 a barrel.
Traders are watching for news from the meeting of Opec oil-producing nations in Vienna, with some member states keen to agree on a production cut to drive up prices.
“We’re looking for a sufficient cut to balance the market, equally distributed between countries,” said Saudi Arabia’s oil minister, Khalid al-Falih, before the meeting.