The coronavirus-delayed Tokyo Olympics will cost at least an extra $2.4 billion, organisers said Friday, with the unprecedented postponement and a raft of pandemic health measures ballooning an already outsized budget.

The extra costs come as officials work to build enthusiasm for the first Games postponed in peacetime, insisting the massive event can go ahead next year even if the pandemic is not under control.

But more spending, on top of the previous budget of about $13 billion, could further harden public opinion in Japan, where polls this year showed a majority of people think the Games should be postponed again or cancelled together.

Tokyo 2020 said an additional $1.5 billion would be needed for operational costs related to the delay, with another $900 million in spending on coronavirus countermeasures.

The extra costs will be split between Tokyo, the organising committee and the national government. The International Olympic Committee will not be chipping in, but has agreed to waive its sponsor royalty fee for the first time, organisers said.

Organisers have tried to scale back elements of the Games, offering fewer free tickets, scrapping athlete welcome ceremonies and making savings on mascots, banners and meals, but so far they have cut just $280 million in spending.

And on Thursday, they said 18 percent of Olympic tickets sold in Japan will be refunded, with domestic fans demanding their money back on about 810,000 of the 4.45 million tickets sold in the country.

Organisers hope to now resell those tickets, and demand for seats at the Games was high before the pandemic.

But enthusiasm has since waned, with a poll in July revealing that just one in four people wanted to see the event held in 2021, and most backing either further delay or cancellation.