The coronavirus-delayed Tokyo Olympics could cost $1.9 billion more than its original budget of $13 billion, a 15 percent increase, a report said Sunday.

The Olympics organisers will formally decide the increased budget for the Games as early as mid-December after communicating with the Japanese government and the host city Tokyo, the Yomiuri Shimbun reported, citing unnamed Olympic sources.

The 2020 Games were pushed back a year as Covid-19 spread around the globe, and are now scheduled to open on July 23, 2021.

But the delay has thrown up a plethora of new costs, from rebooking venues and transport to retaining the huge organising committee staff.

With many countries experiencing second or even third waves of infection, there have been doubts about whether the event can be staged, but organisers and Olympic officials insist it can be done safely.

The extra 200 billion yen ($1.9 billion) on the pre-coronavirus estimate of 1.35 trillion yen ($13 billion) comes despite organisers last month slashing $280 million by cutting everything from staffing to pyrotechnics, but the new figure does not include costs of the coronavirus-related measures, the report said.

Officials expect the virus-linked measures will be paid by the Japanese government, it said.

Plans for a lower-key, lower-cost Olympics were unveiled in September, with fewer free tickets, athlete welcome ceremonies being scrapped and savings on banners, mascots and meals.

The report comes after a senior official on Friday said Tokyo Olympics test events will resume in March and a decision on fan attendance will be made in the spring.

Organisers and officials are considering a long list of possible virus countermeasures that they hope will make it possible to hold the Games, even if a vaccine is not available.

International Olympic Committee chief Thomas Bach earlier this month said he was "very confident" the Games will have fans.

But enthusiasm for the Games appears to have waned in Japan, with polls over the summer finding just one in four Japanese people wanted to see them happen, and most backing either a further postponement or outright cancellation.

Officials of the Tokyo Olympics organising committee could not immediately be reached for comment.