Japan's Shinzo Abe on Friday said he was resigning because of poor health, ending a tenure as the country's longest-serving prime minister in which he sought to revive an economy stricken by deflation and push for a stronger military.

His abrupt departure triggers a leadership battle in his Liberal Democratic Party (LDP) over the next few weeks. The winner will likely stick to Abe's reflationary "Abenomics" policies that had mixed results in resuscitating the world's third-largest economy.

Abe has battled ulcerative colitis for years, and two recent hospital visits within a week had raised questions about whether he could stay on in until his term ends in September next year.

Despite the deepening concerns about his health, news of Abe's resignation sent tremors through Tokyo financial markets. Japan's main stock market, which has more than doubled under Abe, fell some 2% before recovering, while the yen rose on concerns of a return to deflation.