China September HSBC PMI well below flash estimate

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China's factory activity expanded at a slower-than-expected pace in September, a private survey showed on Monday, calling into question the strength of the recovery in the world's second largest economy.

The HSBC Purchasing Managers' Index (PMI) came in at 50.2 – significantly below the flash estimate of 51.2, but a touch higher than 50.1 in August. A reading above 50 indicates expanding activity and one below signals contraction.

"There are still a lot of structural headwinds ahead. This is as good as it gets for the time being. It reflects the stimulus over the summer but don't expect too sharp an acceleration from here," said Frederic Neumann, MD and co-head of Asian economics research at HSBC.

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While new domestic orders remained flat from the previous month, external demand was a bright spot. New business from overseas clients increased for the first time in six months, with managers seeing stronger demand from Europe and the United States.

Don't expect too much from China's factories

Manufacturers' restocking process, meanwhile, continued but remained relatively slow.

Zhiwei Zhang, chief China economist at Nomura, said the marginal improvement from August reinforces his view that the economic recovery is unsustainable.

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"We continue to expect the economy to peak in the third quarter and resume its downtrend thereafter as the policy screws are tightened again," Zhang said.

Ting Lu, China economist at Bank of America Merrill Lynch, said the final HSBC reading was a surprise, noting there is little to explain the gap between the flash and preliminary readings.

"This is the first time there's such a big difference between final reading and flash reading. It implies that the final ten days of September were quite weak. But I don't really see why, there are no signs of a sharp slowdown," he said.

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"In any case, we put more emphasis on the official PMI, which has a larger sample size," he added. The official PMI data will be released on October 1.

Lu said he too expects the positive impact of the fiscal stimulus measures unveiled in July will soon begin to fade, noting that it is not be enough to sustain upward momentum into the fourth quarter.

By CNBC's Ansuya Harjani; Follow her on Twitter @Ansuya_H