General Motors Corporation shares reportedly fell nearly 5% on Tuesday before the New York stock exchange's opening bell [14.30GMT], after dealers started quoting the automaker's bonds as if they were already junk-rated.

Reuters said GM shares fell 4.8% to $US28.27 on the Inet electronic brokerage system, down from its New York Stock Exchange close of $29.69.

The news agency noted that, on March 16, GM warned its 2005 earnings will be as much as 80% below its prior forecast due to slumping North American car sales.