Chinese imports plunged 20 percent in September, casting doubt on the strength of domestic demand in the world's second-largest economy, while oil fell after the West's energy watchdog forecast a global supply glut would last through 2016.

The Toronto Stock Exchange's S&P/TSX composite index <.GSPTSE> ended down 119.63 points, or 0.86 percent, at 13,844.73. Six of its 10 main groups fell.

It had risen to 14,000 last week after starting October around 13,000, largely on the back of gains in the energy and materials sectors. The exchange was closed for a public holiday on Monday.

"The whole rebound in energy and commodities is still very much a toss-up," said Elvis Picardo, strategist at Global Securities in Vancouver. "The fundamentals are very mixed and there are just so many moving parts."

Oil prices, which had sunk 5 percent on Monday, initially gained on Tuesday but settled lower after the International Energy Agency rekindled fears the market remains oversupplied.

The most influential decliners on the index included Canadian Natural Resources Ltd (>> Canadian Natural Resources Limited), down 4.8 percent to C$30.49, and Cenovus Energy Inc (>> Cenovus Energy Inc), which declined 3 percent to C$21.24. The overall energy group fell 2.6 percent.

The materials group fell 1.9 percent, with First Quantum Minerals Ltd (>> First Quantum Minerals Limited) down 10 percent to C$7.77 and Teck Resources Ltd (>> Teck Resources Ltd) declining 9.4 percent to C$8.73.

Prices for copper and gold also slipped.

The country's two main railway companies also weighed, with Canadian National Railway (>> Canadian National Railway Company) off 3 percent to C$78.00 and Canadian Pacific Railway (>> Canadian Pacific Railway Limited) down 3.4 percent at C$196.85.

Global's Picardo said those slips could be a reaction to the Chinese data.

"If you extrapolate that to lower commodity demand and lower commodity shipments ... that could be having some kind of tangential effect," he said.

On the positive side, a mix of consumer names and telecom stocks moved higher. Convenience store operator Alimentation Couche-Tard (>> Alimentation Couche-Tard Inc) added 2.3 percent to C$61.25 and telecom company BCE Inc (>> BCE Inc.) gained 0.7 percent to C$55.92.

(Reporting by Alastair Sharp; Editing by Chizu Nomiyama and James Dalgleish)

By Alastair Sharp