A five-bedroom house in Las Vegas sold in mid-July for $499,000, double the price it went for three months ago. In Phoenix, a similar house sold this month for $600,000, gaining $273,000 since March.

Bubbles are inflating in Nevada and Arizona even as housing in the rest of the country recovers at a more sustainable pace. Gains in the two desert cities are the biggest since the height of the real estate boom, just before their plunge to the bottom of the national housing collapse. This year, Las Vegas and Phoenix have topped the nation in price increases, according to the S&P/Case-Shiller property-value index.

“They’re clearly in bubbles,” said Karl Case, one of the creators of the index. “What can go up can go down -- real quick.”

In May, Phoenix prices jumped 21 percent and in Las Vegas, they rose 23 percent from a year earlier. Nationally, home prices were up 12 percent from a year ago, the most since the beginning of 2006, according to the S&P/Case-Shiller index of 20 cities. Price gyrations in Phoenix and Las Vegas aren’t likely to spread and probably don’t signal another national calamity, said Daren Blomquist, vice president of data firm RealtyTrac.

“The markets where you see wild swings in prices are destination spots, warm places where people want to vacation, like Las Vegas and Phoenix,” Blomquist said. “The rest of the country likely will continue to do well, regardless of what happens in those cities.”

Regional Cycles

There have been regional boom-and-bust cycles before, with home prices in Boston falling 17 percent in a more than four- year decline ending in 1992, and California values plunged 27 percent in six years before bottoming in 1996.

The bust that began in mid-2006 cut 62 percent in the value of Las Vegas homes and 56 percent in Phoenix.

Private-equity firms, hedge funds and real estate investment trusts buying distressed houses to rent have helped push up values in cities hard hit by the housing crash, including Phoenix and Las Vegas. They’ve raised at least $18 billion and bought more than 100,000 properties since 2011.

In Las Vegas, cash deals made up 60 percent of all transactions in June, according to research firm DataQuick Information Systems Inc.