The first Tokyo Olympics test event of 2021 will be postponed due to travel restrictions under Japan's coronavirus state of emergency, media reported Wednesday.

The artistic swimming test event -- which will double as the sport's final qualifier for the Games, and is set to feature around 10 countries -- was scheduled to be held at the Tokyo Aquatics Center from March 4-7.

It could now be held in April or May, according to Japanese media outlets citing sources close to the matter.

The International Swimming Federation (FINA) and Japan Swimming Federation (JASF) have determined travel restrictions on foreign nationals coming into Japan would make the event too difficult to organise, the reports said.

FINA and JASF did not immediately respond to requests for comment, and Tokyo 2020 organisers said they would not address "rumours".

Japan's borders are currently all but closed to foreign visitors, with Tokyo and other parts of the country under a state of emergency until at least February 7.

Athletes coming to Japan to prepare for the coronavirus-postponed 2020 Games had been exempt from the entry ban, but the government revoked the privilege earlier this month.

The artistic swimming event was set to be the first test event to be held with anti-virus measures in place.

In December, Tokyo 2020 chiefs unveiled a 53-page anti-virus rulebook that they say will allow the Games to be held safely without a vaccine, even if the pandemic is not yet under control.