Defaults on commercial mortgage-backed securities issued at the height of the credit bubble will more than quadruple from their current levels under conditions in the US economy expected by the commercial real estate industry, according to a report from Fitch Ratings.

Borrowers would default on an average of 17.2 per cent of securitised commercial mortgages over 10 years if the US economy dips into a recession with 0.2 per cent contraction in growth, compared with current very low default rates of 4 per cent, a rise of 330 per cent.