The US-based Gerontology Research Group says 111-year-old Sakari Momoi from Saitama City, near Tokyo, is now the world’s oldest man.
The previous record holder, Alexander Imich, passed away in New York on Sunday morning.
Mr Momoi was born just one day after Imich, on 5 February 1903.
He is a retired school teacher and was honoured with a medal for his long service to education.
Officials at Guinness World Records are now checking whether Mr Momoi can be certified as the world’s oldest man.
Mr Imich, who was born in Poland but lived at a Manhattan senior residence since 1986, was certified in April.
A retired chemist and parapsychologist, he fought the Bolshevik Revolution and survived the Holocaust before immigrating to the United States from the Soviet Union in 1951.
Editor-in-chief of Guinness World Records, Craig Glenday, said in a statement: “What an incredible life Dr Imich led – fighting the Bolsheviks as a teenager, earning a PhD in the 1920s, surviving a Soviet labour camp, losing much of his family to the Nazis and pursuing a successful career as a chemist and parapsychologist.
“To live such an extraordinarily long and rich life is a testament to good genes, a healthy lifestyle and a positive mental attitude.”
Interviewed by US television about the secret of his long life, Mr Imich once said: “I don’t know, I simply didn't die earlier. I have no idea how this happened.”
He reportedly exercised regularly, ate sparingly and never drank alcohol.
According to the New York Times, he has left his body to medical research in his will.
Dozens of women were older than Mr Imich and the oldest of them, the world’s oldest person, is 116-year-old Japanese woman Misao Okawa, who lives in Osaka City.
