US home prices could plunge as much as 20% within the next year as soaring mortgage rates bring the housing market to a standstill, a prominent economist said Thursday.

Existing-home sales declined for the eighth consecutive month in September, falling 1.5% month-over-month to an adjusted annual rate of 4.71 million, according to the National Association of Realtors. The slump is the longest since 2007. Sales are down nearly 24% compared to one year ago.