* China Jan-Sept property investment +5.8 pct y/y
* Sept only +7.8 pct y/y - Reuters calculations
* Jan-Sept sales +26.9 pct by floor area, Sept only +34 pct
* New construction growth slows significantly from August (Adds analyst comments, quotes NBS official )
BEIJING, Oct 19 September's investment in Chinese real estate showed its strongest growth since May as booming construction, sales and prices contributed handsomely to third quarter economic expansion of 6.7 percent - offsetting stubbornly weak exports.
Property investment rose 7.8 percent in September from a year earlier, compared with 6.2 percent in August, according to Reuters calculations based on data issued by the National Bureau of Statistics (NBS) on Wednesday.
But real estate developers may have become more cautious of taking on new developments, fearing a fall in sales momentum if the government imposes more tightening measures to prevent a property bubble, analysts say.
New construction starts fell 19.4 percent in September month, suggesting sentiment among builders may have already started to cool.
"Today's data showed developers are relatively cautious on new projects, because land has become rather expensive now, and such a strong sales...