LATEST results continue to affirm that mainland economic growth is slowing, ending a three-decade run of double-digit expansion, after the official purchasing managers' index (PMI) slipped to its lowest reading in 18 months of 50.1 in December from 50.3 a month earlier.

Hong Kong's HSBC posted a similar decline in its flash PMI reading at 49.6 in December, down from 50.0 in November and the first deterioration in operating conditions since May.

According to the HSBC, both factory output and new orders declined slightly in December compared to the previous month.

China is heading for its slowest full-year economic expansion since 1990. A combination of excess factory capacity and falling prices for raw materials on global markets has pushed the mainland's manufacturing sector into deflation since 2012.

The weaker Hong Kong Bank PMI reading was partly a result of a renewed fall in new business volumes placed at Chinese manufacturers in December. Though only slight, it was the first reduction in new orders since April, the bank said.

The decline was largely driven by softer domestic demand, as exports rose for an eighth month in a row and at a slightly quicker rate than in November. As a result of lower overall new business, manufacturers cut production for the second successive month in December.

"As seen in the flash reading earlier, domestic demand led the slowdown as new orders contracted for the first time since April 2014," said HSBC China economist Hongbin Qu.

"Price contraction deepened. Today's data confirmed the further slowdown in the manufacturing sector towards year-end. We believe that weaker economic activity and stronger deflationary pressures warrant further monetary easing in the coming months," he said.