Bermuda-based property insurer Catlin said it did not yet know what impact Hurricane Sandy would have on it due to the sheer size of the storm and the many different types of claims it has created.
The company compared the US 'superstorm' to the New Zealand earthquake, Japanese earthquake/tsunami and Thai floods in 2011.
It said "existing catastrophe models are unlikely to predict the quantum of insured damage with a high degree of certainty".
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The losses to Catlin are expected to be clearer when the group reports its 2012 full-year results.
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The firm saw gross premiums rise by 11% in the first nine months of the year as prices went up and its took on new business.
However, this rise was slightly flattered by changes in its accounting methods in the US, with like-for-like sales up 8%.
The firm said its London hub continued to respond to favourable underwriting opportunities as they arose, posting an 8% rise in the period to the end of September.
It saw a 27% increase in gross premiums written by its US arm, reflecting the impact of the accounting change relating to quota share reinsurance treaties written by the division.
Excluding the impact of the accounting change, gross premiums written by the US hub grew by 12%, due to rate increases and new business written, particularly in energy, casualty and reinsurance classes.
The company saw strong growth across all its product groups except aerospace, where gross premiums fell by 1%.
It put this down to continued rate pressure for airline business as well as delays in the number of satellite launches during the period.
Rates continued to increase for many classes of business, particularly catastrophe-exposed business.
Average weighted premium rates across the group's underwriting portfolio increased by 5% during the nine-month period.
Average weighted premium rates for catastrophe-exposed business increased by 9%, while average weighted premium rates for non-catastrophe classes rose by 2%.
