Sompo Holdings Inc. agreed to buy Bermuda-based insurer Endurance Specialty Holdings Ltd. for about $6.3 billion (¥637.5 billion), in the company's biggest acquisition as it expands further outside Japan.

The Japanese insurer will pay $93 a share in cash, or 43 percent more than Monday's closing price of $64.96. The acquisition is subject to the approval of Endurance's shareholders and Sompo plans to complete the acquisition by March 2017, the Tokyo-based company said Wednesday.

Sompo, which largely sat out a multi-billion-dollar acquisitions spree by its peers in the past two years, is joining others in expanding outside the country to counter slowing growth at home. Dai-ichi Life Insurance Co. bought Protective Life Corp. last year, and Sumitomo Life Insurance Co. agreed to purchase Symetra Financial Corp. for about $3.8 billion.

Endurance shares surged 35 percent in New York Tuesday after the Nikkei newspaper reported a deal was imminent and the insurer confirmed it was in talks. Sompo closed 2.7 percent higher in Tokyo.

Endurance is a specialty insurance group with operations in insurance and reinsurance in a range of nations, including the U.S., U.K. and Bermuda.