NEW YORK (CNN/Money) - Thirty-year mortgage rates fell to the lowest level in 31 years as interest rates have fallen along with stock prices, but economists warned Thursday that rates may be nearing a bottom.

Freddie Mac reported that the 30-year mortgage loan rates averaged 6.34 percent this week, with an average of 0.6 of a point payable up front to the lender. This is the lowest level for 30-year fixed-rate loans since the firm began tracking mortgage rates 31 years ago.

The 30-year fell from an average of 6.49 percent last week and was well below 7.03 percent a year earlier.

The 15-year fixed-rate mortgage averaged 5.76 percent, down from 5.93 percent last week and 6.58 percent a year ago. It was the lowest level since Freddie Mac started tracking the 15-year loan in the summer of 1991. The 15-year averaged half a point up front.

One-year adjustable-rate mortgages averaged 4.31 percent, down from 4.50 percent last week and 5.72 percent a year ago. The one-year adjustable rate has not been this low since Feb 25, 1994, when it hit 4.25 percent, the mortgage lending company said.

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"Investors, concerned with the stock market, are putting more of their money into Treasurys," said Robert Van Order, chief international economist with Freddie Mac. "This, in turn, drives down the cost of borrowing. As a result, we are experiencing record-breaking low mortgage rates that are fueling yet another rush to refinance."

"I would...be surprised to see rates fall much lower than today's figures," Van Order added. "For that to happen, the stock market would have to tumble even further than it already has."

Freddie Mac (FRE: down $2.39 to $56.20, Research, Estimates), or Federal Home Loan Mortgage Corp., is a publicly traded company the government established in 1970 to provide a flow of funds to mortgage lenders. It buys mortgages from banks, bundles them and then resells them as mortgage-backed securities.

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Its products, and the products of other similar entities, have become increasingly popular as an alternative to government-backed bonds, particularly with international investors.