Chinese factories enjoyed their best performance this year, the latest purchasing managers indexes (PMIs) also showed on Monday, but economists focused on the eurozone's grim outlook which was worse than any projection in a Reuters poll.
The Markit PMI fell to 47.9 from 49.2 in March, a five-month low and confounding the forecast for a rise to 49.3.
Optimism from this weekend's deal to boost the International Monetary Fund's crisis-fighting firepower quickly evaporated and worried investors sold the euro and bought safe-haven German and US government bonds.
"Today's dismal PMI figures clearly indicate that the eurozone economy remains in dire straits," said Martin Van Vliet, senior economist at ING.
"Our base case scenario is still for a gradual return to modestly positive growth in the second half of this year, but with the lingering debt crisis and the ongoing drag from fiscal policy, the risks are clearly skewed to a more protracted recession."
Grim times for manufacturers
European factories had their worst month since June 2009. Companies said their order books were shrinking and they were cutting jobs in reaction to falling demand.
The overall index slipped further below the 50 threshold that divides growth from contraction.
Politics added to the sense of concern about Europe on Monday. France's presidential election was thrown wide open by the surprisingly high score of a far-right candidate in the first round vote while the Dutch government was set to resign in a crisis over budget cuts.
Industrialised and emerging nations promised another $430 billion to boost the IMF's lending power this weekend, doubling the size of its war chest to fight crises in case Europe's problems worsen.
Global finance chiefs pressed Europe to put in place economic reforms needed to extinguish its sovereign debt crisis, with an increasing sense that the eurozone will have to do more to encourage economic growth instead of just cutting budgets.
The PMIs pointed to worsening demand for goods, with order books shrinking at a faster rate in April.
"There are no real drivers of growth here, which suggests that although the overall rate of decline is modest at the moment, we could see it continue to worsen in coming months," said Chris Williamson, chief economist of PMI compiler Markit.
Economists polled by Reuters last week estimated the eurozone economy shrank 0.2% in the first quarter, and will decline 0.1% this quarter.
Williamson also highlighted the very severe contraction taking place in eurozone economies outside the two largest, France and Germany, raising questions about the effectiveness of harsh austerity measures.
"Tax revenues are going to be low, and unemployment is going to carry on rising, so are these deficit fighting policies working?" he said.
The eurozone's manufacturing PMI also came in below all forecasts from economists, plumbing 46.0 in April - its lowest reading since June 2009 and down sharply from 47.7 in March.
On the plus side, the factory PMIs suggested inflation pressures are easing following a rise associated with oil prices earlier in the year, with the output price index hitting a six-month low of 50.5, from 51.2 in March.
"It does suggest that policymakers ought to be more concerned about the growth outlook than the inflation outlook at the moment. Demand is so weak that companies just can't push through price rises," said Williamson.