Housing prices jumped by more than 9 percent in Nassau County and made modest gains in Suffolk County as a shortage of homes left buyers with scant options.

Homes in Nassau sold for a median price of $470,000 in October, up 9.3 percent from a year earlier, the Multiple Listing Service of Long Island reported Friday. In Suffolk County, the median price increased by 3 percent from a year ago, to $339,830.

It would take 4.7 months to sell all listed homes in Nassau and 6.1 months in Suffolk at the current pace of sales. A balanced housing market has a six- to eight-month supply, brokers say.

“That’s a seller’s market,” said Joe Moshé, broker/owner of Plainview-based Charles Rutenberg Realty. “There’s more buyers out there right now than inventory, so the prices are going up based on competitive bidding.”

Across the Island, sellers listed 12,982 homes last month, a 21 percent year-over-year decline and among the lowest levels since 2004. By contrast, when the Island’s real estate market started to slow in mid-2008, there were nearly 32,000 homes for sale.

The number of closed home sales declined year-over-year by 7.1 percent in Nassau and 2.8 percent in Suffolk last month.

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Despite the rising prices, some Long Island homeowners hesitate to list their homes, said Cynthia McKenna, managing broker at Keller Williams Realty in Hauppauge.

In some cases, homeowners are frustrated that values haven’t rebounded to their previous peaks; in others, they don’t have enough equity to afford another home, she said. In mid-2007, median home prices reached record highs of $502,500 in Nassau and $420,000 in Suffolk.

“Homeowners are still saying that it’s not where they want to sell, it’s not high enough,” she said.

Yet prices have risen so much in the last few years, McKenna said, that “on the flip side of it, you have buyers who are saying, ‘I’m not paying these prices.’ ”

In some cases, buyers are bidding over asking prices, McKenna said. But when they seek appraisals to qualify for mortgage loans, the appraisers don’t always agree with those high valuations, so the price needs to come back down, McKenna said.

Uncertainty about the economic impact of Donald Trump’s stunning upset in the presidential race could cause some people to “wait and see,” at least temporarily, Moshé said.

“I think it all comes down to, to what extent is our country going to have a confidence level in Mr. Trump? If we have that feeling that he’ll be OK, then you’ll see the market spike again,” Moshé said. “On the converse side, if there’s more fear that this country is going to go backwards, people are going to pull back.”