Two people attending the Tokyo Olympics from overseas have been admitted to hospital with COVID-19, a Tokyo 2020 spokesperson said on Thursday, as daily cases in the host city and Japan as a whole hit new highs.

The Japanese capital, where pandemic restrictions are mostly voluntary outside the "Olympic bubble", announced a record 3,865 daily infections on Thursday, up from 3,177 a day earlier.

Daily cases nationwide topped 10,000 for the first time, domestic media reported.

This week's spike in cases prompted the government's top medical adviser to urge a "stronger, clearer" message" about the growing risks from the pandemic, including to the increasingly strained medical system.

Games spokesperson Masa Takaya told reporters neither Games-related case was serious and that a third hospitalised person had already been discharged, declining to give details.

Organisers announced 24 new Games-related infections, including three athletes, taking the total since July 1 to 193.

Competitors in the July 23-Aug. 8 Games and other attendees from around the world must follow strict rules to prevent any spread of the virus within the bubble or to the wider city. Spectators are banned from most venues.

"As far as I'm aware, there is not a single case of infection spreading to Tokyo's population from the athletes or Olympic movement," International Olympic Committee spokesperson Mark Adams told a daily media briefing.

But experts worry that holding the Games sends a confusing message to the public about the need to limit their activities to contain the virus as the highly transmissible Delta variant of the coronavirus spreads. Only 26.5% of residents of Japan are fully vaccinated and testing is scant.

"The biggest crisis is that society does not share a sense of risk," Japan's top medical adviser Shigeru Omi told a parliamentary panel on Thursday. "The numbers (for Tokyo) surpassed 3,000 and this may have some announcement effect. Without missing this chance, I want the government to send a stronger, clearer message."

The surge spells trouble for Prime Minister Yoshihide Suga, whose support ratings are at their lowest since he took office last September, ahead of a ruling party leadership race and a general election this year.

Omi said vaccinations would help, but other factors could fuel infections, including the prevalence of the Delta variant, weariness of restrictions, summer holidays and the Olympics.

Taro Kono, the cabinet minister in charge of the vaccination rollout, which has hit supply snags recently, told the panel that all those who wanted shots should be able to get them by October or November.

The Japan Medical Association urged the government to take steps to avoid an explosive outbreak of the virus, including ensuring sufficient vaccine supply, Kyodo news agency reported.

More than 60% of Tokyo hospital beds available for serious COVID-19 cases were filled as of Tuesday, city data showed.

Many people have grown weary even of the relatively loose restrictions imposed under the city's fourth state of emergency since the pandemic began, making them less effective.