Japan is expected to extend emergency coronavirus measures in Tokyo and several other regions by about three weeks, according to officials, as the country struggles to rein in a fourth wave of infections less than two months before the Olympics.

The state of emergency – the third in the capital since the start of the pandemic – was called in late April and was originally due to end on 11 May, but was extended until the end of this month, as restrictions on businesses failed to make a dent in infections. Media reports said the latest extension could last until 20 June.

Infections have fallen in Tokyo in recent days, but the daily caseload is still too high to justify an end to the measures, according to medical experts, while hospitals are contending with a record number of critically ill Covid-19 patients.

There is also evidence that people are lowering their guard after weeks of restrictions, according to the economy minister, Yasutoshi Nishimura, who is overseeing the country’s virus response.

“In Osaka and Tokyo, the flow of people is starting to creep up, and there are concerns that infections will rise,” Nishimura said Friday at the start of a meeting with government health experts.

The prime minister, Yoshihide Suga, who has described the situation as “highly unpredictable,” was expected to announce the extension in Tokyo, Osaka and seven other prefectures later in the day.

While Japanese authorities do not have the legal powers to impose European-style lockdowns, the measures currently in place are the toughest yet. Restaurants and bars face fines if they refuse to stop serving alcohol or to close at 8pm. A cap on attendance at sports events and concerts, and requests for people to avoid unnecessary outings and travel are also expected to stay in place.

On Thursday, Tokyo reported 684 cases, 159 fewer than a week earlier, and 11 deaths, metropolitan health officials said.

Despite the decrease, the head of the Tokyo Medical Association, Haruo Ozaki, said daily cases in Tokyo needed to be brought to below 100 to prevent another surge during the Olympics.

“I believe there is a need to extend the state of emergency until that figure is reached,” Ozaki told reporters this week, according to the Asahi Shimbun newspaper. “Unless the figure is brought down to that level, there will be a major rebound in new cases in July and August, when the Olympics are to be held.”

Japan has recorded about 735,000 Covid-19 infections and 12,759 deaths – one of the worst death tolls in the region – since the start of the pandemic. Only about 6% of its population has received at least one vaccine dose since its troubled rollout began in mid-February, and most people will still be unprotected during the Olympics.

Signs that more contagious variants are spreading in Japan, coupled with vaccination delays and pressure on medical staff, have triggered calls for the Tokyo 2020 Games to be cancelled.

The government, organisers and the International Olympic Committee [IOC], however, insist that every precaution has been taken to ensure a “safe and secure” Games.

The IOC has vowed to go ahead with the event even if the host city is still covered by emergency restrictions. In an interview this week, Dick Pound, a senior IOC member, said: “Organisers have now changed gears and they’re in the operational part of it. Barring Armageddon that we can’t see or anticipate, these things are a go.”

This week the head of a doctors’ union in Japan warned that the Games, due to open on 23 July, could lead to the spread of Covid-19 variants.

Naoto Ueyama, chairman of the Japan Doctors Union, said the IOC and the Japanese government had underestimated the risks of allowing 15,000 Olympic and Paralympic athletes from more than 200 countries – as well as about 80,000 officials, journalists and support staff – to enter Japan this summer.

“All of the different mutant strains of the virus which exist in different places will be concentrated and gathering here in Tokyo,” said Ueyama, who works at a hospital near Tokyo. “We cannot deny the possibility of even a new strain of the virus potentially emerging.

“If such a situation were to arise, it could even mean a Tokyo Olympic strain of the virus being named in this way, which would be a huge tragedy and something which would be the target of criticism, even for 100 years.”

A recent commentary in the New England Journal of Medicine said the IOC’s determination to proceed with the Games was “not informed by the best scientific evidence”.

The journal added that IOC “playbooks” spelling out restrictions covering athletes, journalists and Olympic staff were “not built on scientifically rigorous risk assessment, and … fail to consider the ways in which exposure occurs, the factors that contribute to exposure, and which participants may be at highest risk”.