They spoke from Japan to a full session of the IOC membership meeting online.
Estimates in Japan say the delay will cost $ 2 billion to $6 billion, with Japanese taxpayers picking up the bills. Olympic officials have not given any overall cost estimate.
The opening ceremony for the Olympics will be on July 23, 2021. However, women's softball and soccer will open on July 21, men's soccer on July 22, and archery and rowing on July 23.
On July 24, the first full day after the opening, the first medal event will be the women's 10-meter air rifle.
Unlike the large, public celebration of a year ago, local organisers at the last minute have put together a small, non-public event for Thursday inside the new national stadium to mark one year to go. Organisers have teased a possible appearance of the Olympic flame.
IOC President Thomas Bach said earlier this week that "multiple scenarios" are being thought about to pull off the Olympics next year. He said empty stadiums were an option, but not a preference, in the long list of possibilities.
"It includes all different countermeasures: quarantine, you name it," he said.
"But, Olympic Games behind closed doors is clearly something we do not want.
"We are working for a solution of the Olympic Games which, on the one hand is safeguarding the health of all the participants, and on the other hand is also reflecting the Olympic spirit.