CANADA STOCKS-Hefty losses in key TSX sectors over commodities, global fears

(Updates throughout with commentary, market reaction, details)

* TSX down 186.32 points, or 1.28 percent, to 14,407.25

* All of the TSX's 10 main groups declined

By Solarina Ho

TORONTO, July 7 (Reuters) - Canada's main stock index tumbled more than 1 percent on Tuesday to levels not seen since January, as worries at home and abroad drove miners, oil and gas companies, and banks sharply lower.

The three sectors make up some two thirds of the index's weight. Nine of the index's 10 heaviest drags belonged to the three groups.

First Quantum Minerals plunged 12 percent to C$13.94, while Toronto-Dominion Bank declined 1.1 percent to C$52.15.

Materials, home to mining companies, sank 4.0 percent, to their lowest level since December, while the financials sector fell 1.3 percent to its weakest level since March.

Gold and copper prices fell to multi-month lows due to instability created by the Greek debt crisis and a stock market rout in China.

"It's tough to get excited about the commodities, with Canada having so many of them, given what's going on with China, Greece," said Ian Nakamoto, director of research at MacDougall, MacDougall & MacTier.

"Commodities depend on robust world wide demand, and we don't have that right now...It's affecting things like Canadian banks, which I always view as a reflection of what's going on with the economy and the spill-over effects."

At 11:12 a.m. EDT (1512 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 186.32 points, or 1.28 percent, at 14,407.25.

All of the index's 10 main groups were mired in red.

Domestically, Canada's trade deficit widened in May to its second-largest on record as exports fell for the fifth month in a row, the latest in a string of disappointing data that points to an economy struggling to cope with the impact of cheap crude prices.

Energy stocks slid 1.6 percent to levels not seen since mid-January. Canadian Natural Resources fell 1.1 percent to C$32.96.

Crude prices, which plunged as much as 8 percent on Monday, extended those losses on Tuesday, falling some 3 percent.

Gold futures fell 1.9 percent to $1,151 an ounce. Copper prices declined 5.2 percent to $5,297 a tonne.

Also weighing on the materials group was Silver Wheaton Corp's 9.3 percent slide to C$20.15 after the mining finance company said it may face tax payments of more than $200 million following a reassessment "proposal" from Canada's tax authority.

Declining issues outnumbered advancing ones on the TSX by 219 to 26, for a 8.42-to-1 ratio on the downside. The index was posting 2 new 52-week highs and 16 new lows.

(Reporting by Solarina Ho; Editing by Chizu Nomiyama)