The eurozone's private sector shrank in September for the first time in two years as the debt crisis continued.
Markit's purchasing managers' index (PMI) of activity dropped to 49.1, from 51.5 last month. A reading below 50 signals a contraction.
Chris Williamson from Markit said: "The recovery has finished, we are now contracting.
"Things will deteriorate further in the coming months." Factory output in the 17 countries that use the euro contracted for the second month running.