Property and casualty (P&C) insurers in the US recorded a net underwriting income of $US4.8 billion ($7.1 billion) in the June half, down 9.6% from a year earlier, ratings agency AM Best says in a report.

The weak performance is the result of a 5.6% rise in loss adjustment expenses and losses, which outpaced the 3.8% increment in net earned premiums.

Pre-tax operating income was flat at $US33.1 billion ($49 billion) and net income declined 2.4% to $US32.7 billion ($48.4 billion).

Catastrophe losses accounted for 4.5 percentage points of the combined ratio of 97.4%, up from 4.2 points last year.

The AM Best data represents 97% of P&C net written premiums in the US market.