This was reported by the Kyodo agency.

#BREAKING: Japan PM Abe announces his resignation at press conference https://t.co/JbgXNdmYe8pic.twitter.com/BhCP0RYwgn

- Kyodo News | Japan (@kyodo_english) August 28, 2020

The agency clarifies that Abe intends to remain in office until a successor is chosen.

Earlier, NHK TV reported that Abe plans to leave the post due to health problems.