Japanese swimming great Kosuke Kitajima is hoping a wave of public support will help Tokyo secure the 2020 Olympics as he contemplates the end of his glittering career.

The four-time Olympic champion, 30, said it would be a "dream come true" to welcome the Games to his native city, touted as the unofficial favourite ahead of next month's vote in Buenos Aires.

Breaststroker Kitajima, dubbed the "Frog King", was heavily involved in the Japanese capital's bid for the 2016 Games, when it lost out to Rio de Janeiro.

But some reports say Tokyo, which has sold itself as a "safe pair of hands", now has the edge over rivals Madrid and Istanbul. The 100-strong International Olympic Committee will make the final decision on September 7.

"Of course I remember what happened last time, but I don't think that the public had as much interest in the Olympics coming to Tokyo then as they do now," Kitajima told AFP in an interview.

"I think what Japan achieved at the 2008 and 2012 Olympics had a really big impact on the Japanese people. Sport is something real that you can't manufacture, and the results in those Olympics really resonated with the Japanese public."

After equalling their record gold haul in 2004, Japan maintained their place in the top 10 nations at Beijing 2008 and despite the 2011 earthquake, tsunami and nuclear disaster, they recovered to earn their highest ever overall medals tally in London last year.

"It has been said that Tokyo is the favourite," Kitajima said. "The athletes are really promoting the bid and are really involved in it. I see the effort they are putting in, and I would love for it to be successful.

"I was involved in the 2016 bid and it was disappointing that we didn't get it, so hopefully this time we can. I was born in Tokyo, so for me it would be like a dream come true."

Kitajima, who won gold in the 100m and 200m breaststroke at both the 2004 and 2008 Olympics, returned to Tokyo last year having spent three years living and training in the United States in preparation for the London Games.

"I was able to see Japan's qualities from living overseas," he said. "I was able to realise how good Japan is -- the food and the lifestyle. I love the United States, and I was able to live there without any stress, but there are a lot of things I love about Tokyo.

"The Olympics would be a good chance to promote Japan to the world. We are an island, so we don't really have so many chances to communicate or interact with people from other countries.

"This is a great chance for Japanese people to meet different people, and for foreign visitors to see Japan."

Whether Kitajima will have another chance to shine on the Olympic stage, however, is in question and he admitted "the end is getting closer" for his top-level swimming career.

The Japanese icon has been experiencing diminishing returns since missing out on an individual medal in London last year, and he managed only a sixth-place finish in the 100m breaststroke at last month's world championships in Barcelona.

"If you only look at the results then it may seem that I didn't do very well, but I was able to perform at a high level compared to the start of the year," Kitajima said of his performance in Barcelona, where he broke two world records and won two world titles a decade earlier.

"I started training late so I was just happy to be able to participate. It was a great opportunity to be able to compete at the world championships."

And although retirement may not be upon him just yet, Kitajima knows he cannot go on forever.

"I'm not sure yet, but the end is getting closer," he admitted. "I've been able to experience a lot of things and make a lot of friends through swimming, so I'm satisfied with what I've accomplished so far. But the end is coming and it's getting hard to set goals for myself.

"I can still continue to be an athlete and teach children and be involved in the sport, but I won't be able to perform at the high level that people expect of me. But I don't want to just say that I will retire completely.

"I am happy to continue as an athlete, but if I can't focus on my efforts and be satisfied with my results, that would be the end."