Concerns about his health have grown this week after he went to hospital twice. Officials from the governing Liberal Democratic party (LDP) had tried to quash speculation that Abe may be unable to serve out the rest of his term. This was due to end in September 2021.
One of Abe’s hospital visits is known to have lasted almost eight hours.
The Japanese leader is known to suffer from ulcerative colitis, a chronic condition.
The severity of his condition was partly responsible for forcing him out of office after just a year during his previous term as prime minister in 2007.
Abe’s deputy, finance minister Taro Aso, is expected take over as acting Prime Minister.
However, his resignation is almost certain to spark a leadership race in the LDP.
The Japanese Prime Minister made his most recent hospital visit on the same day he became Japan’s longest-serving leader.
Shinzo Abe broke the record for consecutive days in office set by his great uncle, Eisaku Sato, half a century ago.
A senior LDP member told Kyodo that Abe’s condition appeared to have flared up again but that he was “already on the mend”.
The official, who was not named, added: “I cannot imagine he will step down.”
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He said: “It’s premature to talk about ‘post-Abe’, as he still has over a year left in his term.”
Media have quoted government sources as saying Mr Abe would consult doctors again possibly over the phone.
They said the doctors would be consulted on Friday before he is due to speak to reporters at 5pm local time.
The Japanese Prime Minister is also expected to defend his handling of the coronavirus pandemic amid an apparent second wave of new infections in Tokyo.
Mr Abe has not briefed the media on the coronavirus crisis since mid-June.
However, he will reportedly outline new measures to fight the pandemic.
Reports say the Prime Minister will pledge to secure enough vaccines for the country’s entire population by early next year should one be available.