Insurance giant QBE estimates Superstorm Sandy will cost it around $US350-450 million, despite its reinsurance arrangements.
QBE has a substantial part of its business in the United States, and says the storm has triggered a flood of claims in its property, casualty, reinsurance and marine and energy businesses.
It says it agrees with market commentary that the insured loss from the storm could be in excess of $US20 billion.
Sandy hit some of the United States' most densely populated areas when it made landfall at the end of October.
The storm damage has blown-out QBE's previous catastrophe provisions, with the company now allowing for 12 per cent of net premiums in large individual risk and catastrophe claims, up from the previous estimate of 10.5 per cent.
QBE says it has also incurred extra losses from its crop insurance business due to a severe drought across much of the US.
The insurer has also had to up its provisions for large individual risks from previous forecasts.
The extra insurance claims have pulled QBE's expected profit margin down to around 8 per cent, from a forecast of 12 per cent or more made in August.
QBE is forecasting a profit of at least $US1 billion for the 2012 calendar year - up 30 per cent on last year, but well down on previous expectations.
City Index's chief market analyst Peter Esho says QBE is building a bad reputation with investors for large negative surprises.
"Instead of making a profit of $US1.6billion this year as market consensus estimates were pointing too, QBE now hopes for pre-amortisation earnings of around US$1billion," he observed in a note.
"That's not necessarily a bad number, it's just that the market is now starting to completely lose trust with management and more importantly the board." QBE shares were down 11.3 per cent to $11.41 by 11:19am (AEDT).