Negative news from Nortel Networks Corp. and slumping commodity prices sent Toronto stocks plunging today. The Toronto Stock Exchange’s S&P/TSX composite index dropped 287.69 points, or 3.37%, to 8,247.33. This was the market worst closing since Dec. 31.

The energy and industrials sector sagged more than 3% while telecoms, utilities, and health-care endured more than 1% declines. In fact, all of the TSX’s 10 sub-groups ended lower, led by a 9.42% plunge in the technology sector.

Nortel has fired its three top executives, and is saying that accounting problems – already under investigation – are worse than previously reported. Its shares plunged $2.18, or 28.76%, to $5.40 with 100 million shares changing hands.

Meanwhile, the materials sector shed 4.91% with the mining sub-group down 6.08%, while gold-mining stocks fell 6.5%. Metals stocks took a hit on news that credit controls in China could curb China’s desire for metals.

This accelerated a downturn in metals prices, which were already under pressure from a rally of the U.S. dollar. Today, the greenback rallied ahead of tomorrow’s first-quarter U.S. GDP report. Analysts expect the report to reflect a strong economic showing for the U.S.

U.S. stocks also sank today. The concerns over China and Nortel also had an adverse impact south of the border. The Dow Jones industrial average fell 135.56 points, or 1.29%, to 10,342.60. The Standard & Poor’s 500 Index dropped 15.70 points, or 1.38%, to 1,122.41, and the Nasdaq Composite Index fell 42.99 points, or 2.12%, to 1,989.54.