TORONTO, Aug 5 (Reuters) - Toronto's main stock index plunged more than 300 points on Tuesday morning as a broad sell-off in oil and other key commodities knocked the index to its lowest level since late March.
The Toronto Stock Exchange's S&P/TSX composite index .GSPTSE was down 343.02 points, or 2.5 percent, at 13,153.51.
Only five of the TSX index's main groups were lower but a massive 6.2 percent decline in the resource-heavy materials group and a 5.2 percent fall in oil issues knocked the market for a loop.
Among oil issues, Canadian Natural Resources (CNQ.TO) and Suncor Energy (SU.TO) fell as the price for U.S. crude oil dropped 0.8 percent to around $120.50 a barrel after touching as low as $118 a barrel earlier in the session as worries about a tropical storm in the Gulf of Mexico lessened.
Canadian Natural dropped C$4.35 to C$76.93, and Suncor Energy was down C$3.47 at C$52.65.
Resource shares were led lower by fertilizer producers Potash Corp (POT.TO), which dropped C$18.49 to C$188.50, and Agrium Inc (AGU.TO), which fell C$5.91 to C$83.86. Agrium is set to release quarterly results later in the week. ($1=$1.04 Canadian) (Reporting by Scott Anderson; Editing by Peter Galloway)