Buyers clearly felt the clock ticking in October, snapping up existing homes at a seasonally adjusted annual rate of 6.10 million units, according to data released Monday by the National Association of Realtors (NAR).

It represented a 10.1% gain compared to the previous month and a 23.5% year-over-year increase in such activity. . “Many buyers have been rushing to beat the deadline for the first-time buyer tax credit that was scheduled to expire at the end of this month, and similarly robust sales may be occurring in November,” said Lawrence Yun, NAR’s chief economist.

In early November, Congress approved an extension of the credit, which had been set to expire Nov. 30, to April 30, 2010, and expanded it (with a lower credit amount) to existing-home owners who sell their house, provided they have lived in it for at least five years.

October’s sales surge also reduced existing-home inventories by 3.7% to 3.57 million, which is good news for builders who have had trouble competing against such a high volume of homes for sale. At the current sales pace, that translates into seven months’ of supply of existing homes on the market. 

According to Yun, that qualifies as the “lowest level [of supply] in over two-and-a-half years” and equivalent to what was on the market in February 2007.

Existing-home pricing remains a problem for builders, though; the median price for a new home in October was $173,100, according to NAR data. That is significantly lower than the median price for new homes, which was $204,800, based on U.S. Census Bureau data. (September represents the most recent data available; new-home sales for October will be released Wednesday, Nov. 25.)

Alison Rice is senior editor, online, at BUILDER magazine.