An indicator of Chinese manufacturing activity has decline in a sign of challenges facing communist leaders who have promised sweeping reforms in the slowing economy.

An industry group, the China Federation of Logistics & Purchasing, said Wednesday that its purchasing managers index for December declined to 51 from the previous month's 51.4. The measure is a 100-point scale on which numbers above 50 indicate increasing activity.

"There still is downward pressure on economic growth," said economist Zhang Lijun in a statement that accompanied the report.

A Communist Party plan issued in November promised to revitalize the economy by injecting more competition into industries dominated by state-owned companies. This week, the ruling party announced the formation of a body led by President Xi Jinping to oversee regulatory changes.