Sales of previously owned homes nationwide unexpectedly plunged in January, an industry survey showed on Friday, fresh evidence the housing market has yet to find stable ground.

The National Association of Realtors said sales fell 7.2 percent to an annual rate of 5.05 million units, sharply below market expectations for a 5.50 million unit pace.

December sales were revised slightly lower to 5.44 million pace from 5.45 million units. Compared to January last year, sales of existing homes were up 11.5 percent.

The Warren Group reported Tuesday that single-family home sales in Massachusetts jumped almost 12 in January year-over-year percent to 2,153 from 1,926 in January 2009. Condominium sales also soared 25 percent to 1,011 from 807 in January 2009.

"Today’s figure is certainly not good news in terms of sales," said Lawrence Yun, chief economist for the NAR.