*TSX down 291.14 points, or 2.1 pct, at 13,328.05
*All 10 sectors down sharply (Updates with details, comments)
TORONTO, March 15 (Reuters) - Toronto's main stock index tumbled to a seven-week low on Tuesday morning as Japan faced a potential catastrophe after an earthquake-crippled nuclear power plant exploded and sent low levels of radiation floating towards Tokyo.
Fears of a radiation disaster hammered world stock markets and fueled a broad sell-off in commodities such as oil, base-metals and even safe-haven gold as investors raced to liquid assets like cash. [MKTS/GLOB]
All 10 of the Toronto index's sectors dropped sharply. The energy group was down 2.6 percent, materials was off 2.8 percent, and financials dropped 2 percent.
Among the individual heavyweight decliners, Cameco Corp (CCO.TO), the world's second largest uranium miner, sank almost 8 percent to C$29.19.
Suncor Energy (SU.TO) declined 2.4 percent to C$41.11, Barrick Gold Corp (ABX.TO) fell 2.3 percent to C$48.51, First Quantum Minerals (FM.TO) dropped 3 percent to C$107.85, and Bank of Nova Scotia was down 1.9 percent at C$57.23.
"We've broken below technical levels across markets globally here, so the risk is to the downside," said Fergal Smith, managing market strategist at Action Economics.
The Toronto index has closed below the 50-day moving average around 13,700 for the past two days, paving the way for a retest of the January and December lows around 13,100, Smith said.
At 10:16 a.m. (1416 GMT), the Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was down 291.14 points, or 2.14 percent, at 13,328.05. Earlier, it fell as low as 13,237.93, its lowest level since Jan. 25.
"Investors are stepping back for the moment during this bout of uncertainty," Smith said, noting the U.S. Federal Open Market Committee meeting later in the day could provide some direction.
"More broadly, economic growth has remained supportive of the market, but while there's risk of a Japanese nuclear meltdown, investors are going to try and be risk averse until that uncertainty is clarified."
($1=$0.99 Canadian) (Reporting by Claire Sibonney; editing by Peter Galloway)