Retail sales in the US fell last month, confounding expectations that they would remain flat.
The disappointing figures sent an immediate jolt through London's stockmarket, with the FTSE 100 index down more than 80 points.
US shares are expected to move lower when the New York market opens at 2.30pm London time.
The US Commerce Department said retail sales fell 0.4% in April, against a flat forecast.
The data followed a worse than expected 1.3% drop in March.
January and February had shown gains after six successive months of decline, raising hopes that consumer spending was recovering.
The negative trend of the past two months undermines the growing optimism that the global economy was starting to see the "green shoots" of recovery.
Instead analysts are wondering whether the world is poised for a "double dip".
"Following some better sentiment about the economy and markets, today's figures suggest that the V-shaped recovery is not in the bag," said ING analyst Rob Carnell. "'Double dippers' may take some solace in figures like these."
The FTSE 100 looks like recording its third successive decline today, having added 27% over the past two months.
The index is down 82.51 points at 4343.03.
