Toyota Motor Corp's debt rating was cut by Fitch Ratings, the automaker's first downgrade in 10 years, as the slump in US car sales drags down earnings at the company with the industry's best credit.

Fitch cut Toyota's senior unsecured debt rating two levels to AA from AAA with a negative outlook on the company, it said in a report today. The shares dropped 4.6 percent, the most in two weeks, to close at 2,985 yen on the Tokyo Stock Exchange.

A lower debt rating raises borrowing costs for Toyota, potentially hindering its ability to offer interest-free loans to boost sales in the US.