Home sales in Southern California plummeted in September to a two-decade low, and a rash of grim housing-market assessments Tuesday suggested the worst is yet to come, the Los Angeles Times reports.

“We’re on our way down and still picking up speed,” said Christopher Thornberg, a Los Angeles-based economist who four years ago warned that the pace of housing price gains in the region couldn’t be sustained.

The gloom extended to Washington, where Treasury Secretary Henry M. Paulson Jr. called the U.S. housing downturn the “most significant current risk to our economy.” Paulson echoed a prediction by Federal Reserve Chairman Ben S. Bernanke on Monday that the slump would be a “significant drag” on economic growth into next year.

Adding to the sobering picture, the National Assn. of Home Builders said its builders’ confidence index hit a record low. The index, which tracks builders’ views of market conditions and sales expectations for the coming six months, fell to 18 from 20 in August. It has been below 50 — above which indicates a positive industry outlook — since May 2006.

In Southern California in September, home sales in six counties — Los Angeles, Orange, Riverside, San Bernardino, San Diego and Ventura — fell 48.5% from the same month last year. They were at their lowest since DataQuick Information Systems, a real estate service, began compiling such statistics in 1988.

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