TORONTO (Reuters) - Toronto's main stock index fell for a third straight session yesterday as oil and metal prices tumbled on concerns about euro zone debt and weaker growth in China, knocking commodity issues lower.

Teck Resources fell 6.3 percent to C$33.11 and First Quantum sank 6.6 percent to C$64.98 as industrial metals plummeted.

"There's concern that the international economies, in particular China, are slowing down.

People extrapolate that to make the assumption that you're going to see lower commodity prices," said Irwin Michael, portfolio manager at ABC Funds.

Toronto's slide came as China's key stock index tumbled 5.07 percent yesterday to its lowest close in a year. That fall was led by property issues, as retail investors fled the market after a month-long rout sparked by a severe government clampdown on surging property prices.

Investor sentiment was also bruised by concern that efforts to tackle the Eurozone debt crisis could stifle the global economic recovery.

The Toronto Stock Exchange's S&P/TSX composite index ended down 201.97 points, or 1.68 percent, at 11,813. It slumped as low as 11,695.61, its lowest level in a week. Nine of the index's 10 main groups were lower.

A tumble in oil prices hit TSX energy shares, with Suncor Energy down 2.5 percent to C$31.26, while Canadian Natural Resources fell 1.7 percent to C$71.37.

The materials group, home to mining and fertiliser companies, sank 2.8 percent while energy issues fell two percent.

The losses on the TSX were not limited to commodity-linked issues. Also weighing were financials, down 1.3 percent, and industrials, which sank 1.7 percent.

It was the index's third straight session lower.

"People are edgy. You know the old saying, sell in May and go away? It's still May," said Mr. Michael.

"Clearly, it looks like it's a bit of a buyers' boycott. A lot of people are stepping away, not being sure what to do. When that happens it's a question of supply and demand," he said.

In individual company news, Toronto-Dominion Bank sank 1.9 percent to C$71.98 after it said it would buy troubled US lender South Financial Group Incfor $191.6 million to build on its presence in the US Southeast, especially Florida.