The attacks on the twin towers of World Trade Center could cost insurers more than $5 billion, making the suspected terrorist attack on the 110-story skyscrapers the most costly man-made catastrophe ever, analysts said yesterday.

While it is expected to take years for the insurers to sort out the losses, dozens of insurers are expected to bear the cost of the damage, including the cost of the towers, which collapsed and burned after being struck by two hijacked airliners, as well as damage to the surrounding area and the cost of office furnishings and equipment.

Reinsurance companies may eventually pay the most for the attack, since underwriters usually protect themselves from potentially crippling losses by splitting the risks -- and the premiums -- of big policies. Big reinsurers like Lloyd's of London, the Munich Reinsurance Company, Berkshire Hathaway and Swiss Re could be the most exposed, analysts said, though it was not immediately clear whether any of the companies were affected.

In Zurich, Swiss Re shares fell 13 percent yesterday, the Baloise Insurance Group dropped 11.1 percent and Swiss Life 7.8 percent.