Asian and European stock markets have tumbled after US values returned to levels not seen since the start of the year.
A bruising session on Wall Street on Wednesday saw technology stocks take a particular hammering – building on losses of recent weeks.
The Dow Jones Industrial Average lost 2.4%, meaning it had erased all 2018’s gains by the close.
The tech-dominated Nasdaq lost over 4% to enter a so-called ‘correction’.
That is because it is now more than 10% below its August peak.
Shares in Asia followed the US lower, with Japan’s Nikkei closing 3.7% down on Thursday.
The FTSE 100, which has little exposure to the technology sector, was 1% lower in early deals.
Bond prices also rose, sapping yields, as traders sought safe-haven investments.
Market experts blamed disappointing outlooks in tech company results for stoking jitters over world economic growth and future corporate profitability.
There are several factors behind those gloomier forecasts.
Top of the list is the US trade war with China.
Investors are also facing the expectation of higher US interest rates, which would boost borrowing costs for not only US firms and consumers but also many struggling emerging market economies with dollar-linked debt.
There is also Brexit, the suspected murder of journalist Jamal Khashoggi by Saudi Arabia and a big budget dispute between Italy and the EU in Brussels.
A plunge in oil prices, with Brent crude trading at $75 a barrel down from over $80 in recent weeks, has taken value from energy stocks too.
Makoto Sengoku, market analyst at Tokai Tokyo Research Institute, said: “This mess of bad factors has made it difficult for markets to seize a chance to turn up.”
Neil Wilson, chief market analyst at Markets.com, pondered whether the long-awaited bear market had begun.
He wrote: “It looks like the poor US housing stats yesterday acted as (a) warning and investors took fright.
“We’re in a period of pressure building to the downside as we get more down days than up and the breadth of the decline is important as is the volume.
“However whilst the recent spike in volatility may be seen as meaning we’re past the peak, there may yet be a few breaths left in this old bull.”