European shares trimmed gains on Thursday afternoon after worse-than-expected manufacturing data from the United States cast a shadow on expectations that the world's largest economy was on a steady recovery path.

The pace of growth in the U.S. manufacturing sector unexpectedly slowed in February, with the Institute for Supply Management saying its index of national factory activity fell to 52.4 from 54.1 the month before.

At 3:08 p.m., the FTSEurofirst 300 <.FTEU3> index of top European shares was up 0.9 percent at 1,085.41 points.

(Reporting By Francesco Canepa)