The Japanese government is under pressure to reverse course and hold the Tokyo Olympics behind closed doors as Covid-19 cases rise in the capital.

After bottoming out at fewer than 400 cases a day in mid-June, the number of new diagnoses has climbed to almost 600 a day, raising fears of a full-blown surge when the games are held between July 23 and August 8.

The increasing cases count has highlighted the risk taken by Yoshihide Suga, Japan’s prime minister, in choosing to ignore his medical advisers and allow the games to go ahead with up to 10,000 fans in stadiums.

It also reflected the growing presence in Japan of the more infectious Delta variant of Covid-19 and the delayed progress of its inoculation campaign, which has administered a first dose to 24 per cent of the population.

The organisers of Tokyo 2020 said they have delayed a ticket lottery until Saturday as the debate on spectators comes to a head. Japan decided just two weeks ago to let some fans attend.

Suga lifted a Covid-19 state of emergency in Tokyo on June 20. Since then, the city has been under a “quasi state of emergency”, during which restaurants are asked but not compelled to stop serving alcohol by 7pm and to close by 8pm.

The restrictions were meant to end this weekend, but officials said the government was considering whether to maintain them throughout the Olympics. If cases keep rising, Suga could also be forced to declare a full emergency.

Many Olympic events have been scheduled for the evening to avoid the worst heat of the Japanese summer, but it will be hard to justify stadiums full of spectators if all of the nearby restaurants have been asked to close.

Katsunobu Kato, chief cabinet secretary, insisted that the decision on spectators was one for the organisers and the governor of Tokyo rather than the government alone. “We will make an appropriate judgment based on the state of infections and the [virus countermeasures] in place,” he said.

Speaking after his ruling coalition fell short of a majority in Tokyo municipal elections at the weekend, Suga said the government would have to decide soon on whether to extend the quasi state of emergency.

Separately, Shinzo Abe, former prime minister, attacked those who support cancelling the Olympics as “anti-Japanese”. He singled out the Communist party and the centre-left Asahi newspaper.

In an interview with local magazine Hanada, Abe said that the emotion of the games and Japanese athletes winning medals would confirm the bonds between the Japanese people. He added that a successful games would have “historic meaning” and that the country had a duty to go ahead.