China's official manufacturing purchasing manager's index, a key measure of factory activity, fell 0.3 percentage points to 49.8 in January, state media reported Sunday, according to dpa.
It was the first time the index dropped below 50 since October 2012, marking increasing downward pressures on the economy, official Xinhua news agency said.
A figure above 50 generally means a positive outlook in the manufacturing sector.
Falling commodity prices and sluggish market demand contributed to the drop, said Zhao Qinghe, a senior statistician of the National Bureau of Statistics.
China's economy grew by 7.4 per cent in 2014, the weakest growth in 24 years, according to official figures released last month.