Mortgage sales across the country sank 21.2% in September month on month as worried buyers delayed their foray into the property market, according to Australian Finance Group's (AFG) findings.

Mortgage broker AFG said the past two years have recorded an 8.5% weakening of mortgage sales during September, with this year's figures showing that overall sales continued to plummet by 21.2% - two-and-a-half times the established seasonal average.

NSW copped the brunt of the declining climate at 27.4%, Victoria fell by 21.9%, Queensland by 20.9% and Western Australia by 22.3%.

Mark Hewitt, general manager of sales and operations, AFG, said public concern about global debt markets and the unknown potential impact of sub-prime repercussions was causing buyers to hold off. "This is particularly true in NSW, which is the most vulnerable state to mortgage stress and also the most sensitive to report media coverage," he said.

However, Hewitt added that he believed the underlying market is still strong, particularly in Victoria. "We're seeing higher levels of confidence in property than we have for some time."

For the first time, the average mortgage size of sales in Victoria passed the $300,000 mark, standing at $304,000, which is a 13% increase from the beginning of the year.

AFG also found that one in five property buyers opted for fixed mortgage rates to safeguard themselves against fluctuating interest rates, bringing last month's fixed rate mortgage figure up from 18.3% to 20.4%.