(Updates throughout with market reaction, details)
* TSX down 87.53 points, or 0.66 percent, to 13,219.43
* Eight of the TSX's 10 main groups fall
TORONTO, Oct 1 (Reuters) - Canada's main stock index fell on Thursday, as an early rally among oil and gas names quickly lost steam and trading moves mirrored equity losses on Wall Street.
The TSX had capped off a volatile third quarter in the previous session with a 2 percent rise and looked set to extend those gains, but the moves were short lived. Investor sentiment remained cautious over China's economic growth and the timing of an interest rate hike by the Federal Reserve.
At 11:43 a.m. EDT (1543 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 87.53 points, or 0.66 percent, to 13,219.43.
Of the index's 10 main groups, eight were mired in negative territory, with declining issues outnumbering advancing ones on the TSX by 163 to 77, for a 2.12-to-1 ratio on the downside.
Valeant Pharmaceuticals International shares, which have been badly bruised over the last 1-1/2 weeks due to accusations of drug price gouging, was the biggest drag on the index, sinking 3.1 percent to C$230.77. The overall healthcare group, however, eked out a 0.8 percent win.
Potash Corp shares followed, stumbling 3.5 percent to C$26.46, while the overall materials group, home to resource and mining firms, retreated 1.8 percent.
Energy stocks swung between positive and negative territory throughout morning trading. Imperial Oil Ltd fell 1.4 percent to C$41.69 while Encana Corp rallied 3.4 percent to C$8.88.
In corporate news, Bombardier Inc shares fell 3.6 percent to C$1.61 after the struggling plane and train maker said it was exploring the sale of a stake in any of its business units, not just rail, to ensure it can finish its much delayed CSeries jet.
SNC Lavalin Group stock was up 2.1 percent to C$38.78. The engineering and construction company settled with the African Development Bank Group after allegations that former employees had ordered illicit payments to secure contracts for projects in the region. (Reporting by Solarina Ho; Editing by James Dalgleish)