Factory activity weakened across much of Europe and Asia in December as the U.S.-led trade war and a slowdown in demand hit production in many economies, offering little reason for optimism as the new year begins.

A series of purchasing managers' indexes for December released on Wednesday mostly showed declines or slowdowns in manufacturing activity across the globe.

"We are really seeing a global slowdown into this year, and in Asia, particularly, export-oriented countries are hurting," said Irene Cheung, Asia strategist at ANZ.