Slowing premium growth may force Japan's insurance companies to seek more takeovers abroad to counter declining profits in the world's most rapidly aging country.

The seven biggest casualty insurers, including Tokio Marine Holdings Inc., this week reported a combined first-quarter profit of ¥70.8 billion, 37 percent lower than a year ago. Net premium income fell 0.6 percent on declining demand for auto insurance because fewer people drive.

Japan is the first developed country to register more annual deaths than births, with the elderly set to outnumber children two to one within five years, according to the health ministry. To counter falling premiums at home, Tokio Marine is buying Philadelphia Consolidated Holding Corp., and Dai-ichi Mutual Life Insurance Co. agreed to buy a stake in Tower Australia Group Ltd.