Chinese factories ramped up activity in March for the first time in nine months, official data showed Friday, offering a positive signal for the health of the world's second-largest economy.

The result surprised observers and suggested Beijing's efforts to boost demand were having a bigger-than-expected impact.

Zhao Yang, China economist for Nomura, said the data was "much stronger" than forecast and showed "across the board" improvement.

This "means a rebound could be stronger and more lasting than we initially thought".

China's economy is a vital driver of global expansion. But it grew only 6.9 percent last year, its weakest rate in a quarter of a century.

The key manufacturing sector has been struggling for months in the face of sagging global demand for Chinese products.

But the official Purchasing Managers' Index (PMI) from the National Bureau of Statistics (NBS), which tracks activity in factories and workshops across the vast nation, rebounded to 50.2 for March, showing that it was ticking up.

It was the highest number and first expansion since June 2015. The result also surpassed the median expectation of 49.4 predicted by economists in a Bloomberg News survey.

A reading above 50 signals expanding activity in the sector, while anything below indicates contraction.

Beijing has been trying to re-tool its economy to encourage domestic consumption, and move away from reliance on investment and overseas buyers.

But recent policy easing as it seeks to avoid a hard landing has encouraged a resurgence of investment, and ratings agency Standard & Poor's lowered its outlook for China Thursday as credit floods the economy.

The PMI figure follows February's 49.0.

Investors watch the index closely as the first available official indicator of the country's economic health each month.

NBS analyst Zhao Qinghe said the March number showed "some positive signs have started to emerge" following the Lunar New Year holiday.

"Manufacturing production and the market warmed up as companies started working after the Spring Festival and supply-side reform accelerated."

- 'Upside surprise' -

There was also some relatively good news from the private Caixin Purchasing Managers' Index, which puts a greater emphasis on smaller firms.

That came in at 49.7, its highest reading in 13 months, the Chinese financial magazine said in a joint statement with data compiler Markit.

It said the figure showed "only a fractional deterioration in the health of the sector", as companies cited an improvement in orders. Although weak foreign demand "remained a drag" on growth, it added.

The market reaction was muted, with the benchmark Shanghai Composite Index closing up just 0.19 percent.

NBS analyst Zhao cautioned the PMI figures could be partially attributed to seasonal factors, as well as to a rebound in fixed-asset investment and the property market.

Economists have long said one of China's main structural problems is an over-reliance on government infrastructure projects.

"We should be aware that there remain many difficulties in companies' production and operation," he said.

Firms were still facing tight financing, insufficient demand and rising labour costs, Zhao added.

Analysts pointed to an increase in government investment as signalled at the March National People's Congress, with ANZ attributing the "upside surprise" to "an acceleration of infrastructure spending and recent pickup in electronic supply chains".

The positive results implied China could achieve 6.5 percent economic growth for the quarter, they added.

But Caixin pointed out: "Firms continued to cut their staff numbers, with the rate of job shedding easing only slightly from February's seven-year record."

Its surveyed manufacturers have shed jobs every month since November 2013 as they downsize to cut costs.

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NOMURA HOLDINGS