* CSI300 -2.2 pct; SSEC -2.2 pct; HSI -3.0 pct
* China Sept flash factory PMI falls to 6-1/2-year low
* Sentiment at Asia's biggest firms tumble on China growth fears
SHANGHAI, Sept 23 (Reuters) - China and Hong Kong stocks fell on Wednesday morning, hit by weakness in global markets and a survey of China factory activity that deepened fears of a sharp economic slowdown.
China's blue-chip CSI300 index fell 2.2 percent, to 3,267.05 points by midday, while the Shanghai Composite Index also lost 2.2 percent, to 3,116.9 points.
Hong Kong's benchmark Hang Seng Index slumped 3 percent in its biggest one-day percentage fall in a month.
"Sentiment was soured mainly by sharp falls in European and U.S. equity markets, and global commodity prices," said Alex Kwok, strategist at China Investment Securities.
"The markets were also hit by China's PMI data released today, which doesn't look good."
China's September flash PMI, which measures activity in the country's factory sector, unexpectedly shrank for the seventh month in a row to the lowest level in 6-1/2 years, a private survey showed.
The latest survey showed that conditions in September deteriorated from August by almost every measure, with companies cutting output, prices and jobs at a faster pace as orders fell.
Fears of a sharp slowdown in China, which already contributed to the U.S. Federal Reserve's inaction on rates, is spilling across the region, and threatens to fan turmoil in global financial markets.
Sentiment at Asia's biggest firms tumbled in the third quarter at record pace due to growing worries about the economic slowdown in China and the risks it poses to the global outlook, a Thomson Reuters/INSEAD survey showed.
All main sectors in China fell, with energy and infrastructure stocks leading the decline.
China's biggest steelmakers such as Baoshan Iron & Steel Co Ltd fell sharply, on fears that economic cooling would sap demand for the metal.
The growth fear was echoed by China Iron and Steel Association, whose vice chairman said on Wednesday that China's steel demand had already peaked.
CITIC Securities tumbled 3.7 percent.
An initial probe found that CITIC, China's biggest brokerage, illegally profited from China's government-orchestrated stock rescue scheme, Bloomberg reported on Wednesday, citing sources.
In Hong Kong, the Hang Seng index dropped 3.0 percent, to 21,146.31 points, while the Hong Kong China Enterprises Index lost 4.3 percent, to 9,414.03.
With the Hang Seng now below 21,400 points - seen by many as a key psychological support level, the index could slide further despite its modest valuations, Kwok of China Investment Securities said.
All main sectors in Hong Kong fell, with energy and materials stocks the hardest hit. (Reporting by Samuel Shen and Pete Sweeney; Editing by Jacqueline Wong)