(Adds details, updates prices)
* TSX down 166.88 points, or 1.28 percent, at 12,849.71
* All of the TSX's 10 main groups fall; energy stocks down 3.3 pct
* Index on track for a 3.6 pct decline over the week
TORONTO, Dec 11 (Reuters) - Canada's main stock index sank further on Friday following a two-day respite as energy stocks tumbled after an oil group warned on slowing demand growth and heavyweight bank shares also fell.
The most influential movers on the index included Royal Bank of Canada, which fell 1.4 percent to C$73.12, and Toronto-Dominion Bank, which declined 0.9 percent to C$53.50.
The overall financials group, 38 percent of the index's weight, retreated 1.2 percent.
Energy stocks lost 3.3 percent, with Canadian Natural Resources down 3.1 percent at C$29.03 and Suncor Energy Inc off 1.9 percent at C$35.01.
Hudson's Bay Co slumped 13.3 percent to C$17.26 after cutting its sales forecast for this year and next in an earnings report late on Thursday.
At 10:11 a.m. EST (1511 GMT), the Toronto Stock Exchange's S&P/TSX composite index fell 166.88 points, or 1.28 percent, to 12,849.71.
That was a fresh 11-week low, with 22 stocks hitting new 52-week lows and 8 names falling for every stock that gained and all 10 main groups weighing.
The index had crashed through the 13,000 level earlier in the week before paring some losses on Thursday. The index is on track for a 3.6 percent loss over the week.
On the positive side, the maker of Ski-Doo snowmobiles and See-Doo watercraft, BRP Inc, advanced 14.1 percent to C$23.02 after reporting soaring profit helped by favorable exchange rates.
U.S. crude prices were down 2.3 percent to $35.92 a barrel, while Brent crude lost 2.8 percent to $38.60 a barrel.
Global oil markets will remain oversupplied at least until the end of 2016 as demand growth slows and OPEC output booms, putting oil prices under further pressure, the International Energy Agency said.
Reporting by Alastair Sharp; Editing by Meredith Mazzilli