The median sales price for all types of homes in the nine-county Bay Area jumped 33 percent to $555,000 in June -- the largest annual increase in at least 24 years, according to a report Thursday.

But in a reflection of the small number of homes on the market, the number of sales dropped sharply in a month when they typically increase, according to the San Diego real estate information service DataQuick.

"Three factors that got us to this amazing yearly price gain are ultratight inventory, ultralow mortgage rates and record or near-record levels of investor purchases," said Andrew LePage of DataQuick. "Now all three are changing in a way that suggests these kinds of price increases won't continue for long."

The June price increase was the largest since the company began recording annual median home sales gains in 1989, he said.

In the South Bay, Peninsula and East Bay, prices for single-family homes saw double-digit increases from the previous June.

Prices jumped 35 percent to $590,000 in Alameda County and nearly 33 percent to $437,000 in Contra Costa County. Prices increased about 17 percent to $750,000 in Santa Clara County and almost 21 percent to $785,500 in San Mateo County.

Even rising prices don't convince everyone to sell. Ed and Peggy Carlisle could have cashed in by selling their home in Danville -- purchased four years ago -- for close to $200,000 more than they paid for it.

Instead, this week they took their home off the market. "It's worth a lot more than we had ever hoped for," said Ed Carlisle, "but we love this place.''

Their agent, Paul Ward of Keller Williams in Danville, said some of his clients would love to sell but can't find a place to buy.

"I've never seen inventory so low as this year," Ward said. "In January and February, it was practically nonexistent.''

Sales fell in June, thanks to rising interest rates and little inventory. In the Bay Area, sales of all types of homes were down more than 9 percent from June of last year, a surprising drop in the midst of the peak home-buying season. The 8,541 sales were nearly 21 percent below the June average, DataQuick reported.

Sales of single-family homes were off 4.6 percent in Alameda County; 10.8 percent in Contra Costa County; 8 percent in Santa Clara County and 13.5 percent in San Mateo County.

In lower-priced areas, investors and move-in buyers are still duking it out, with an investor's cash often carrying the day.

"The only reason that prices are going up is because we have no inventory," said Tara Chinn, at Intero Real Estate in Brentwood.

"I'll have a property listed at a normal price and I'll get 29 offers on it, so it jumps in price. It's not realistic. I try so hard to help first-time homebuyers, but the investors are coming up with $20,000 to $50,000 more in cash, and there's nothing we can do about it."

But as prices rise some investors are buying fewer homes and more homeowners can sell as their houses recover equity lost in the housing crash.

Real estate professionals say they're already seeing gradual increases in inventory this month.

"Inventory levels are starting to gently go up and some of the institutional investors have started to go away," said Keith Robinson, chief operating officer of Better Homes and Gardens Mason-McDuffie in Pleasanton

Over the next few months, that should give move-in buyers a better chance at purchasing a home.

Julie Pavlova, a single mom with three young children, lost out on two homes to offers that were $50,000 and $20,000 more than hers. Now she is buying a home in South San Jose for a little less than its owners' $670,000 asking price.

Her agent, Jessica Martin of Intero Real Estate in Los Gatos, said Pavlova wrote a letter explaining that it was all the money she had for a home, and the owners dropped the price a little to help her buy it.

After selling her townhouse in less than a week in June for $165,000 more than she paid for it a year ago, Pavlova said she shopped around for about month and saw the market getting a little less intense. "I'm not sure if it's interest rates going up or what the reason is," she said. "It's gone down a little bit price-wise, and fewer people coming in with these huge offers. To be outbid by $50,000 -- that's quite a big jump. With this house it didn't happen."

Contact Pete Carey at 408-920-5419. Follow him on Twitter.com/petecarey.