* FTSEurofirst 300 dips 0.8 pct, Euro STOXX 50 down 0.5 pct
* Both benchmark indexes hit one-month lows
* Russia-exposed stocks hit again as sanctions talk builds
* Europe big winner of emerging market exodus -Amundi CIO
PARIS, March 12 (Reuters) - European shares fell on Wednesday, sending benchmark indexes to one-month lows, as mounting worries over China's economic growth rate and persistent tensions in Ukraine spooked investors.
Shares in exporters were among the hardest hit, with German conglomerate Siemens down 1.4 percent and BASF , the world's fifth-largest agrochemicals and seeds maker, sliding 1.2 percent.
A sharp sell-off in metal prices - with copper prices plumbing levels not seen since July 2010 - also weighed on mining stocks, with Glencore Xstrata falling 1.3 percent.
Copper's slump followed China's first domestic bond default which has sparked worries of a possible unravelling of the many loan deals which have used the metal as collateral.
"Markets are on red-alert for the possibility that we'll see more and bigger defaults as time passes," said Jeremy Batstone-Carr, analyst at Charles Stanley. "The bigger concern is that wound up in these defaults is the threat of a Chinese slowdown over and above that which is pencilled in."
At 1530 GMT, the FTSEurofirst 300 index of top European shares was down 0.8 percent at 1,311.22 points.
The index had briefly extended its losses in afternoon trade, falling by as much as 1.5 percent to a one-month low as investors were rattled by the collapse of a building in a largely residential block of Upper Manhattan in New York.
The euro zone's blue-chip Euro STOXX 50 index was down 0.5 percent at 3,076.61 points.
Also hitting sentiment, tensions continued to rise in Ukraine, while European Union member states agreed the wording of sanctions on Russia, including travel restrictions and asset freezes against those responsible for violating the sovereignty of Ukraine.
Shares of companies most exposed to Russia were among the biggest losers, with Finnish tyre maker Nokian Renkaat down 2.9 percent, Austrian lender Raiffeisen Bank International dropping 2.6 percent, and Danish brewer Carlsberg losing 1.3 percent.
The three firms derive 26 percent, 22 percent and 17 percent respectively of their revenues from Russia, according to data from MSCI.
Despite the recent slide, analysts and fund managers remained positive on the outlook for European stocks, which should continue to benefit from strong investment inflows as economic growth is expected to pick up.
"Europe is one of the big winners of the recent flight out of emerging markets, and these trends in flows are usually quite long term as investors such as sovereign funds usually invest with a time horizon of 10 years," said Pascal Blanque, chief investment officer at Amundi, which has 777 billion euros ($1.08 trillion) under management.
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