A Nigerian Olympic delegate became the first visitor to the Tokyo Games admitted to hospital with COVID-19, broadcaster TV Asahi said Friday, as Japan battles to stem rising local infections a week before the showpiece event starts.

The individual, a nonathlete in their 60s, tested positive on Thursday evening at the airport with mild symptoms but was hospitalized because of age and pre-existing conditions, the broadcaster said, without giving details.

Organizers have promised that the games, starting on July 23 after being postponed from last year because of the pandemic, will be "safe and secure."