The 30-year, fixed-rate mortgage averaged 5.78 percent with an average 0.6 points in the week ending Sept. 18, Freddie Mac (NYSE:FRE) said.

A week ago, 30-year, fixed-rate mortgages averaged 5.93 percent with an average 0.7 points. Two weeks ago, the average rate was 6.35 percent.

At 5.35 percent with an average 0.6 points, the 15-year, fixed-rate average also declined, dropping from the previous week's average of 5.54 percent. A year ago, 15-year fixed-rate mortgages averaged 5.98 percent, the report said.

Over five weeks, interest rates for 30-year fixed-rate mortgages have dropped about 0.75 percentage points.

"As a result, mortgage applications surged nearly 58 percent since Aug. 15, largely led by a 122 percent gain in applications for refinancing," said Frank Nothaft, Freddie Mac vice president and chief economist.

Nothaft noted that fixed-rate mortgages "are currently the predominant choice among homebuyers and families looking to refinance."

"Over the first two weeks of September, 95 percent of new applications were for fixed-rate mortgages," he said.