China's manufacturing activity expanded at a slower pace in April, an official factory survey showed on Tuesday, suggesting some loss of momentum for the sector at the start of the second quarter.

The National Bureau of Statistics (NBS) manufacturing purchasing managers' index (PMI) dropped to 50.4 in April from 50.8 in March, above the 50-mark separating growth from contraction and just ahead of a median forecast of 50.3 in a Reuters poll.

The data underlines the challenges facing policymakers even though solid first quarter GDP growth had reduced some of the urgency to ramp up stimulus measures.

New export orders grew at a much slower rate, while employment continued to shrink, the NBS's PMI data showed.

Still, a private Caixin factory survey, which was also released on Tuesday, showed manufacturing activity grew more quickly as new export orders rose, providing a more optimistic outlook than the official data.

Investors expect Beijing to launch more stimulus to support the economy and were waiting for the outcome of a politburo meeting, which is expected to focus on economic affairs this month. (Reuters)