Liberty Mutual Holding Co says profit grew 17% to $US1.25 billion ($1.32 billion) in the first nine months of this year.

Net written premium increased 7% to $US26.84 billion ($28.29 billion), while a 12% rise in gains for personal insurance offset a decline in commercial revenues.

The combined ratio improved 2.3 points to 99.7% and catastrophe losses fell 4.5%.

“While severe storm activity was milder than the prior year, our combined ratio decline was driven by improved core underwriting results,” Chairman and CEO David Long said.

Catastrophes during the period included severe storms in the US, Cyclone Oswald, central European floods, the Alberta floods in Canada and hailstorms in Germany.

Third-quarter earnings increased 3% to $US481 million ($507 million) and net written premium was up 8% on the corresponding period last year.

“The third quarter reflected a continuation of our strategy of growing where we can do so profitably and contracting elsewhere,” Mr Long said.