* Commodities fall as cheaper yuan boosts dollar
* Eight of 10 S&P sectors down, energy stocks weigh
* Industrials and materials stock also hit
* China uncertainty weighs on Apple, GM, Caterpillar
* Indexes down: Dow 1.2 pct, S&P 0.96 pct, Nasdaq 0.95 pct (Adds quote, updates prices)
By Sweta Singh
Aug 11 (Reuters) - U.S. stocks fell in morning trading on Tuesday in a broad retreat, with the Dow down more than 1 percent, as China's surprise devaluation of the yuan pushed the dollar higher and pressured commodity-related stocks.
The yuan fell to its lowest against the dollar in almost three years following what China's central bank described as a "one-off depreciation" that increased unease about the health of the country.
Brent crude was down 3 percent and U.S. crude fell 4 percent following the devaluation by the world's top energy consumer. Prices of commodities such as copper, aluminum, nickel, and zinc slid between 2 and 3.5 percent.
Eight of the 10 major S&P sectors were down, with the energy index and the materials index both lower by nearly 2 percent.
Exxon Mobil's 1.9 percent drop was the biggest drag on the energy index and Freeport-McMoRan's 13.3 percent slump dragged on the materials index.
Concerns around the health of the second-largest economy in the world also weighed on shares of U.S. automakers and industrials. General Motors was down nearly 3 percent, while Caterpillar was down 2.9 percent.
At 11:21 a.m. EDT (1521 GMT) the Dow Jones industrial average was down 211.14 points, or 1.2 percent, at 17,404.03
The S&P 500 was down 20.26 points, or 0.96 percent, at 2,083.92 and the Nasdaq composite was down 48.71 points, or 0.95 percent, at 5,053.09.
"It's all about China today. We were doing so well yesterday and then China came and devalued the yuan and we are back in the ship again," Paul Nolte, portfolio manager at Kingsview Asset Management in Chicago.
Wall Street had climbed on Monday, giving the S&P 500 its biggest increase since May, buoyed by gains in commodity-related shares and optimism over Warren Buffett's deal to buy Precision Castparts.
Nolte believes that markets are trying to align conflicting cues from global economies and the U.S. Federal Reserve, which is widely expected to raise interest rates in September.
"Those two are in opposition to each other. It's hard for the U.S. to be the island in the storm around the world and that why we are seeing markets jump around."
Apple shares were down nearly 3 percent at $116.23 after Jefferies raised concerns about the demand for the iPhone, primarily in China. The stock was the biggest drag on the S&P and the Nasdaq.
Google rose 3.6 percent to $687.34 after it said it would overhaul of its operating structure.
Terex rose 20 percent at $26.20 after the U.S. cranes and mining equipment maker and Finnish rival Konecranes agreed to an all-share merger.
Declining issues outnumbered advancers on the NYSE. On the Nasdaq, 1,837 issues fell and 796 advanced.
The S&P 500 index showed five new 52-week highs and 10 new lows, while the Nasdaq recorded 29 new highs and 60 new lows. (Reporting by Sweta Singh in Bengaluru; Editing by Savio D'Souza)