Japan faces its most serious situation since the Covid-19 pandemic began, the country's top medical adviser has warned.

The government has been urged to send a "clearer, stronger message" about growing risks, including to the medical system.

Olympic host city Tokyo recorded 3,177 new Covid-19 cases yesterday, hitting a daily record high for a second straight day as a spike in infections puts pressure on hospitals.

Nationwide new cases topped 9,500 for the first time, media reported.

"The biggest crisis is that society does not share a sense of risk," top medical adviser Shigeru Omi told a parliamentary panel.

"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 spike in infections adds to worries about the Games, which are taking place under unprecedented conditions including a ban on spectators in most venues.

The surge also 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.

Mr Omi said vaccinations would help contain the virus, but many more factors threatened to cause further rises in infections including the prevalence of the highly transmissible Delta variant, weariness of restrictions, and the Olympics.

Only 26.5% of residents of Japan are fully vaccinated and the rollout has hit supply snags recently.

Many Japanese have worried the influx of athletes and officials for the Games will add to the surge, while experts have warned that holding the high profile sports event sends a confusing message about the need to stay home.

Olympic athletes, staff and media must follow strict rules including frequent testing to prevent any spread of the virus from inside an "Olympic bubble".

Organisers today announced 24 new Games-related Covid-19 cases, bringing the total to 193 since 1 July.

Tokyo is under its fourth state of emergency set to run through the Olympics, but the mostly voluntary measures have proven less effective than in the past.