NEW YORK (CNN/Money) - The U.S. housing market remained red-hot in September, according to reports Friday from the government and the nation's realtors.

The National Association of Realtors said existing homes sold at an annual rate of 5.4 million in September, up 1.9 percent from a revised 5.3 million-unit pace in August. Economists, on average, expected sales at a 5.35-million-unit pace, according to Briefing.com.

"Mortgage interest rates have been on a steady slide since April and reached new historic lows in September, contributing significantly to higher existing-home sales," said David Lereah, NAR's chief economist, in a statement.

Separately, the Commerce Department said sales of new homes rose 0.4 percent to a 1.02-million-unit pace in September from a revised 1.017-unit pace in August. Economists, on average, expected sales at a 990,000-unit pace, according to Briefing.com.

The reports briefly helped U.S. stock prices rise; but stocks soon gave up their gains and were mixed in early trading. Treasury bond prices were mostly higher.

The NAR said the national median existing-home price was $159,000 in September, up 7.9 percent from September 2001, when the median price was $147,400.

The Commerce Department said the median new-home price was $176,300, up 5.9 percent from a median price of $166,400 a year ago.

Rock-bottom mortgage rates in the past year have helped fuel demand for new and existing homes, driving prices higher and helping homeowners recover from the sting of a dismal stock market.

Low rates also fueled a boom in mortgage refinancing, allowing homeowners to lower their monthly mortgage payments or borrow against their increased home equity. This in turn helped support consumer spending, which makes up about two-thirds of the total economy.

But mortgage rates are rising again, threatening to finally cool off the housing market and take one support away from consumer spending. Most economists believe businesses will need to start spending money again in order to help the economy to continue its recovery from a recession that began in March 2001.

Still, mortgage rates have been at 40-year lows; they've got a long, long way to go before they get high enough to douse the housing market.

"Mortgage rates will put a little bit of a brake on housing activity," said Anthony Chan, chief economist at Banc One Investment Advisors, "but it may come precisely as other sectors start to turn around."