Oil prices and stock markets around the world have seen further falls, sparked by the renewed fears over the health of the global economy.
China shares fell 1.5% after the authorities intervened again on the stock market to little effect.
Expectations of a US interest rate rise dimmed after the Federal Reserve said the economy was not ready yet.
On Wall Street, the Dow Jones index opened 1% lower, while markets in Paris and Frankfurt fell more than 2%.
London’s benchmark FTSE 100 index shed 0.56%, while the price of Brent crude oil was down 0.4% at $46.97 a barrel, although US crude recovered from earlier falls to stand 0.6% higher at $41.35.
On August 19, the Fed released minutes from its meeting on July 28-29, showing that one policymaker was ready to vote for an interest rate rise at the meeting.
Overall, the Fed thought conditions for a US rate rise “were approaching”, but the economy was not ready yet.
The Fed’s key interest rate has been kept near zero since December 2008.
There has been speculation that the Fed will raise rates at its meeting in September, and last month Fed chair Janet Yellen said she thought a rate rise this year was likely.
Following the release of the Fed’s minutes, US stocks rallied briefly but then fell back, while the dollar weakened on the currency markets. The Dow Jones index ended August 19 trading down 0.9%.
The committee also cited China as a potential problem, saying that a “material slowdown” in the Chinese economy could affect the US economic outlook.
The FOMC’s meeting came before last week’s action by China to weaken its currency.
After days of volatility, Chinese stock market traded lower once again on August 20, despite Beijing’s efforts to calm markets.
China’s Shanghai Composite closed 1.5% down at 3,735.92 points.
The fall comes after the index saw strong volatility earlier in the week.
Traders appeared not to respond to efforts by the central bank to provide more liquidity to stabilize markets.
In assessing the strength of the US economy, the Fed has been keeping an eye on the US jobs market – where the unemployment rate has been falling and is now 5.3%. However, inflation is still below the Fed’s target of 2%.
The minutes from the Federal Open Market Committee’s (FOMC) July meeting noted that the labor market “had continued to improve, with solid job gains and declining unemployment”.
However, when assessing inflation, it said that “some members continued to see downside risks to inflation from the possibility of further dollar appreciation and declines in commodity prices”.
The FOMC said it would continue to monitor inflation “closely, with almost all members indicating that they would need to see more evidence that economic growth was sufficiently strong and labor market conditions had firmed enough for them to feel reasonably confident that inflation would return to the committee’s longer-run objective over the medium term”.
Inflation figures released earlier on August 20 showed that consumer prices rose by 0.1% in July, and were 0.2% higher from a year ago.
So-called core inflation, which ignores changes in food and energy prices, also rose 0.1% last month, but was up 1.8% over the year.