TORONTO (Reuters) - The Toronto Stock Exchange's main index was hammered by a sell-off in resources yesterday, plunging more than three percent as commodity prices fell, marking its worst day in more than seven months.

The heavyweight energy sector led the slide as oil prices slid on fading concerns over the impact from Hurricane Gustav on the US oil industry.

Oil settled down $5.75 at $109.71 a barrel as reports suggested oil installations in the Gulf of Mexico had weathered the storm with only minor damage. Suncor Energy fell 9.6 percent to C$54.91.

The resource-laden materials sector also yanked the Toronto index lower, as it was hurt by falling prices of gold and other metals, which followed oil's example. Inmet Mining slid seven percent to C$59.50.

The S&P/TSX composite index closed down 471.51 points, or 3.42 percent, at 13,299.74 with all 10 of its main sectors ending lower. It was the biggest one-day percentage loss since January when Bay Street was knocked down by fears over the prospects for the US economy.

The energy and materials sectors, which account for more than half of the index, shed 6.5 percent and 5.9 percent, respectively.

Other laggards included Potash Corp of Saskatchewan , which fell 6.5 percent to C$172.70, while Canadian Natural Resources slumped 6.5 percent to C$84.73. Analysts said that with the threat of Gustav passed, worries had turned to concerns of falling demand in the face of a weak global economic outlook.

The tech sector also crumpled under pressure from worries over lower corporate spending, following comments last week from bellwether computer firm Dell.

BlackBerry maker Research In Motion fell 2.4 percent to C$126.31, while the sector overall gave up 3.4 percent.