The volume of commercial mortgages at risk of default has quintupled since the beginning of 2008 as a deteriorating economy has made it increasingly difficult for shops and businesses to keep up with their payments.

Special servicers, companies that collect payments from borrowers in distress on behalf of mortgage bond investors, reported $23.7bn of mortgages under their care at the end of the first quarter, according to Fitch Ratings.

That was five times higher than the $4.6bn of mortgages needing special servicing at the end of 2007. Servicers experienced an almost 50 per cent increase in the volume of distressed commercial mortgages in the first quarter alone.

Mortgages for multi-family residential properties suffering from the housing downturn represented the largest share of the troubled loans at 31 per cent, said Fitch. However, mortgages for shops and businesses were catching up, with retail loans at 28 per cent of the distressed pools.

“Retail properties were the first property type to see the effects of declining economic conditions and consumer spending,” said Stephanie Petosa, analyst at Fitch. “[We have] observed an increase in defaults of retail loans and expect them to eventually surpass multi-family as the highest property type concentration.”

Mortgages for retail properties such as shopping centres have suffered from bankruptcies of “big box” retailing tenants such as Circuit City and Linens ’n Things, spurring an increase in vacancies and forcing a growing number of borrowers to seek relief from their lenders.

General Growth Properties, the second-largest US mall owner, collapsed earlier this month because it was unable to refinance more than $3.3bn in debt due for repayment this year. The company owns 200 shopping centers.

“Commercial real estate is in a world of hurt and will be for at least the next two years,” said Ross Smotrich, analyst at Barclays Capital. “This is a capital intensive business in which lending capacity has diminished because of the absence of securitization, while the fundamentals are driven by the overall economy so both occupancy and rents are declining.”

Fitch analysts said they expect commercial mortgage defaults to continue to increase this year. At the end of the first quarter, defaults and payments more than 60 days late were at 1.53 per cent of outstanding mortgages. Fitch said they could reach 4 per cent by the end of 2010.