Chinese manufacturing activity increased sharply in July, rising at its fastest pace in more than two years, an official survey has shown, as the world's second-largest economy shows signs of increasing momentum.

The official purchasing managers’ index hit 51.7 last month, the country’s National Bureau of Statistics said in a statement.

The figure was up from 51 in June, and the best since 53.3 in April 2012. 

It was also above the median 51.4 forecast in a survey of nine economists by The Wall Street Journal. 

"We are optimistic about China's economic outlook in the remainder of this year, as the growth momentum is picking up while the inflation remains mild," ANZ Bank economists Liu Li-Gang and Zhou Hao said in a note reacting to the survey.

The index tracks manufacturing activity in China's factories and workshops and is a closely watched indicator of the health of the economy. 

A reading above 50 indicates growth, while anything below points to contraction.

Separately, British bank HSBC said its final PMI reading for July also came in at 51.7, up from 50.7 in June but weaker than the preliminary 52.0 announced last week. HSBC said it was an 18-month high.

Qu Hongbin, HSBC's chief China economist, said small revisions to several sub-indices brought the number down from the preliminary figure.

"Nevertheless, the economy is improving sequentially and registered across-the-board improvement compared to June," he said in a press release accompanying the data. 

"Policy makers are continuing with targeted easing in recent weeks and we expect the cumulative impact of these measures to filter through in the next few months and help consolidate the recovery."

Chinese authorities have since April introduced a series of measures to bolster growth, including tax breaks for small enterprises, concentrated infrastructure outlays, and incentives to encourage lending in rural areas and to small companies.

Chinese economic growth accelerated to a higher-than-expected 7.5% in the second quarter, up from 7.4% in the previous three months, which was the worst since a similar 7.4% expansion in July-September 2012.

The rebound helped relieve concerns that arose earlier this year when growth slowed in the first quarter to its slowest pace in 18 months, prompting authorities to introduce what economists have described as "mini-stimulus" measures.

China in March set its annual growth target for this year at about 7.5%, the same as last year.

In a report on the official PMI, Julian Evans-Pritchard, China economist at Capital Economics said the reading "suggests that economic activity is still being supported by healthy foreign demand along with state-led infrastructure investment and other targeted stimulus measures".