The Games will be held exactly one year later than originally planned, July 24-August 9, 2020.

The Paralympics will start August 24 and run until September 5, also keeping the same slot.

The Games were postponed on March 24 because of the coronavirus outbreak, with IOC president Thomas Bach initially saying they could be held at any time next year until summer.

A statement on Monday said the quick decision was based on three considerations: protecting everyone's health and supporting containment of Covid-19, safeguarding the interests of athletes and Olympic sport, and the global sports calendar.

"I am confident that, working together with the Tokyo 2020 Organising Committee, the Tokyo Metropolitan Government, the Japanese Government and all our stakeholders, we can master this unprecedented challenge," IOC president Thomas Bach said.

"Humankind currently finds itself in a dark tunnel. These Olympic Games Tokyo 2020 can be a light at the end of this tunnel."

Organising committee president Yoshiro Mori said: "Taking this decision promptly will help speed up future preparations ... The Tokyo 2020 Organising Committee will continue to work hard for the success of next year's Games."

Tokyo Governor Yuriko Koike told reporters: "We will once again start make preparations in order to hold a safe and secure Games for athletes and spectators."

"But, at first, we have to defeat the novel coronavirus," she added.

The announcement means that 2021 world championships in several sports, including the showcase Olympic sports of swimming and athletics, must find new dates.

World Athletics said it would push back their 2021 worlds, scheduled for August 6-15 in Eugene, Oregon, by one year.

"Everyone needs to be flexible and compromise and to that end we are now working with the organisers of the World Athletics Championships in Oregon on new dates in 2022 for our World Athletics Championships," World Athletics said.

The aquatics worlds are scheduled for July 16-August 1 next year in Fukuoka, Japan, and the governing body FINA said it would consult with Fukuoka organisers, athletes, TV partners and other stakeholders "to determine the most appropriate solution."

FINA has previously suggested it would look into a new 2021 date rather than moving back one year.

The one-year postponement also allows sports to complete qualifying events postponed over the past weeks owing to Covid-19. Athletes already qualified for the Games will meanwhile keep their spots and quota spots won't change either.

Organisers have also already confirmed that ticket holders can either attend their rescheduled event or request a refund.

The swift decision on the new dates especially relieved local officials.

Sapporo city official Masayuki Nakata said he was glad to hear Olympic marathons and walking events will still take place in summer.

"A spring Olympics would have required totally different adjustments," Nakata told Kyodo News.

The IOC moved the marathon and walking events to Sapporo, the capital of the northern island of Hokkaido due to Tokyo's extreme heat in summer.

Bowing to mounting pressure from athletes and sports bodies amid the global coronavirus pandemic, Bach and Prime Minister Shinzo Abe agreed last week on the postponement of the Tokyo Olympics to 2021.

Japan faces large extra costs through the postponement and hopes that the IOC will help cover them. Japan has said it has spent more than $US12 billion ($A19 billion) overall on the Olympics it was awarded in 2013.

Australian Associated Press