* Yuan falls to lowest since Aug 2011 after Tuesday devaluation
* Asian stocks plunge, regional index at 2-year lows
* Europe markets expected to open lower
* Emerging market currencies fall against dollar
* Commodities nurse losses as deflationary forces loom
By Saikat Chatterjee
HONG KONG, Aug 12 (Reuters) - Asian stocks and emerging market currencies tumbled on Wednesday and commodities fell after China let the yuan fall sharply for a second straight day, forcing investors to seek refuge in safe-haven government debt.
Financial spreadbetters expect Britain's FTSE 100 to open 0.6 percent lower, Germany's DAX to start 0.9 percent lower. France's CAC 40 was seen falling 0.6 percent at the open.
On Wednesday, the People's Bank of China set the yuan's midpoint rate weaker than Tuesday's closing market rate, which had already fallen sharply after China devalued its currency by nearly 2 percent in a surprise move.
The yuan fell further after Beijing released July output and investment data. The currency yuan, which was at 6.4275 to the dollar, weakened further to 6.4398 at 0545 GMT.
The central bank had billed Tuesday's change as a free-market reform but experts suspect it could be the beginning of a longer-term slide in the exchange rate aimed at making China's ailing exports more competitive.
The rapid drop in the value of China's currency - around 4 percent in the last two days - dealt a body blow to appetite for risky assets globally, with equities, currencies and commodities coming under selling pressure as money managers feared it could ignite a currency war that would destabilise the global economy.
MSCI's broadest index of Asia-Pacific shares outside Japan fell 2.1 percent to a two-year low. Stock markets from Australia to Singapore were a sea of red.
"China's currency moves will hurt appetite for risky assets such as equities and commodities," said Rajeev De Mello, head of Asian fixed income at Schroders in Singapore, which manages $10 billion in Asia.
"While it is too early to say whether this is the beginning of a sustained devaluation of the yuan, other central banks may be forced to follow suit and that may trigger a fresh round of currency weakening around the emerging world."
On Wall Street, the Dow fell 1.2 percent and the S&P 500 shed 1 percent as China's currency move added to worries about the global economic outlook and hit companies with large exposure to the country.
Many Western firms have already been reporting slowing sales in China as its economy cools and shares of companies from German auto makers to luxury good makers are expected to come under pressure.
Emerging market currencies from Indonesia to Brazil reeled as investors feared central banks around the world could rush to weaken their own currencies in response to China's move.
That meant only the greenback was left standing tall with the U.S. dollar holding near a two-month high of 125.17 yen , while the broad dollar index was stuck within recent trading ranges.
Currencies considered as China proxies were singled out for special punishment, with the Australian dollar nursing losses at 0.7250 per dollar after falling more than 1.5 perent overnight.
"The bottom line is that we believe investors will orientate portfolios towards more rate cuts rather than currency weakness. Real rates are way too high, in our view," wrote Sean Darby, chief global equity strategist at Jeffries.
Commodities investors worried that prolonged yuan weakness could revive deflationary pressures, with a 19-commodity Thomson Reuters/Core Commodity CRB Index holding near lows not seen since 2003.
U.S. crude oil futures extended their decline with prices at their lowest since March 2009.
Copper and aluminium also hit six-year lows on Tuesday as the cheaper yuan fueled worries the world's top metals consumer would cut back on imports.
Copper posted a modest bounce after the overnight slide, with three-month copper on the London Metal Exchange (LME) edging up 0.7 percent to $5,159 a tonne.
Bonds were the solitary bright spot, with the the benchmark 10-year Treasury note yield holding near a three-month low of 2.09 percent hit overnight.
Its 10-year Japanese counterpart fell to fresh a three-month trough of 0.37 percent. (Additional reporting by Shinichi Saoshiro in TOKYO; Editing by Kim Coghill and Richard Borsuk)