Swiss Re, the world's second-largest reinsurer, said it expected claims from US hurricanes Rita and Wilma of about $750 million and reiterated it would miss its 10-percent growth target on earnings per share this year.
It had scrapped that goal in September after raising claims it expects to pay following Hurricane Katrina.
Swiss Re said it would dip into equalisation reserves to mitigate the claims and still expected to propose a dividend of 2.50 Swiss francs per share for 2005.
Germany's Hannover Re said it would have to cut its 2005 earnings forecast further after assessing the Wilma damage.
"It is to be expected that the forecast has to be cut further," a spokeswoman said, adding that Hannover Re planned to provide a detailed assessment when it publishes third-quarter earnings on November 10.
She said the company was also reassessing the damage caused by other recent hurricanes that have hit the United States in what was the most intense hurricane season on record.
Hannover Re shares fell 1.1 percent to 29.94 euros by 1003 GMT, while Swiss Re shares fared better, down just 0.2 percent at 88.70 francs.
Hannover Re had previously said it aimed to achieve 2005 net profit of at least last year's level of 309 million euros ($369.3 million). That target was set after Hurricane Katrina forced the company to abandon an original goal of earning 430 million-470 million euros in 2005.
The company had also said it was confident it could reach its 430 million-470 million-euro net profit target in 2006.
Dealers said the news was further evidence that the impact of the hurricanes on reinsurers was greater than the market had originally estimated.
"The impact from these storms had initially been underestimated, and this is now the payback for that," a Zurich-based dealer said.
"At least it is not an operative problem, but net costs are going to be up in the short term," he added.
The world's largest reinsurer, Munich Re has so far kept mum about how much of insurers' damage claims it will have to pick up. Munich Re said it would update its assessment along with its third-quarter results on November 7.
This year's hurricane season has spawned three of the most intense Atlantic storms on record: Katrina devastated New Orleans in August and killed an estimated 1,200 people, while Rita hit the Texas-Louisiana border a few weeks later.
While hurting profits, the storms have also given reinsurers more pricing power over their clients, who have been pressing for cuts after a prolonged period of high premiums following the September 11, 2001, attacks in the United States.
Swiss Re said estimates for total insured claims caused by Rita were around $10 billion, with a major part from damage to offshore oil installations, while Wilma was expected to have caused insured claims of between $6 billion and $12 billion.
Credit ratings agency Fitch has said reinsurers may have to pay up to $27 billion for hurricanes Katrina and Rita, but said they were in a strong position to absorb the bill.
Reinsurers take some of the risks that are too big or volatile for insurers to handle alone.