TORONTO (Reuters) - Toronto's main stock index closed lower yesterday, but cut a near-four percent intraday tumble, sparked by a drop in crude futures and worries the Greek debt crisis may widen to other euro zone countries.

The TSX energy sector tumbled 1.41 percent, though losses were four times bigger at one point, as US crude prices fell below $77 a barrel on fears the debt crisis could threaten economic recovery and undercut demand for oil.

EnCana Corp. fell 1.39 percent to C$31.95 and Nexen dropped 2.88 percent to C$22.97.

Heavyweight financials were down by 1.26 percent, with Royal Bank of Canada off 2.68 percent at C$59.57 and Bank of Montreal down 3.05 percent at C$59.07.

The Toronto Stock Exchange's S&P/TSX composite index finished down 32.7 points, or 0.28 percent, at 11,842.43.

Amid the sell-off, the TSX fell 452 points, or 3.8 percent, to 11,422,73, its lowest level since February 25.

By the end of the session, six of the index's 10 main groups had bounced back. But lower energy and financials, two of the most influential sectors, underscored lingering worries over wider contagion from Greece's debt crisis.

Thursday afternoon's rapid slide by the TSX echoed an even sharper plunge by US stocks, with Nasdaq down more than nine percent at one point.

Along with the Greek debt crisis, analysts also cited uncertain UK elections and a large, erroneous trade entered by a a big Wall Street bank as possible reasons behind the session's volatility.

"Some or all of it could have contributed to this." said Ian Nakamoto, director of research at MacDougall, MacDougall & MacTier. "It's a confluence of anxiety."