The unexpected news of Abe's resignation sent Tokyo stocks plunging more than two percent, with the benchmark Nikkei 225 index reversing earlier gains.
Government sources said it was not a worrying situation, Nippon TV reported, while Kyodo News cited people near to the prime minister as saying it was for a regular check-up.
The comment came as Shinzo Abe aims to boost Japan's presence in the promising African market but many businesses are wary of financial and other risks.
Final numbers were not expected until Monday at the earliest.
Washington has decided to deploy 1,500 additional troops to the Middle East amid growing friction with Tehran after Trump pulled out of a landmark nuclear deal and later re-instated tough sanctions.
Akihito, 85, was the first Japanese monarch to take the throne under a post-war constitution that defines the emperor as a symbol of the people without political power.
Some of Japan’s leading companies in Britain have warned that a no-deal Brexit could be a disaster. After meeting May in London, Abe said it was scenario no one wanted to see.
The new five-year defence plan calls for the upgrade of two existing helicopter carriers so that they can launch fighters.
Japanese business is eager for increased access to China's massive market, while Beijing is interested in Japanese technology and corporate know-how.
Abe, who returned to office in December 2012, was re-elected as leader of his Liberal Democratic Party (LDP) last month, putting him on track to become Japan’s longest-serving premier.
About 3,000 tourists stayed overnight at Kansai airport in the heavily populated south-central area of Japan’s main island, Honshu.
The expected victory over ex-defense minister Shigeru Ishiba in the 20 September Liberal Democratic Party (LDP) poll would put Abe on track to become Japan’s longest-serving premier.
Prime Minister Shinzo Abe cancelled an overseas trip to deal with Japan’s worst flood disaster since 1982, with several million people forced from their homes.
Shinzo Abe has spoken to Donald Trump 30 times since he became president and officials say Washington is well-aware of Tokyo’s stance towards Pyongyang.
A survey by broadcaster Nippon TV released on Sunday showed Abe’s support had sunk to 26.7%, the lowest since the conservative lawmaker took office in December 2012.
Abe has denied that he ever instructed officials to give preferential treatment for the establishment of Japan’s first new veterinary school in more than 50 years.
Abe, now in his sixth year in office, had tried to put behind him questions over the sale of state-owned land at a huge discount to a school operator with ties to his wife, Akie.
In his first public comments since an apparent diplomatic breakthrough between North and South Korea, Shinzo Abe has cautioned that talking for the sake of talking is 'meaningless'.
