The US government on Friday sounded alarm about the surge in coronavirus cases in Japan, adding to a chorus of prominent domestic voices - including the governor of Tokyo - who have called for decisive action to avoid an explosive outbreak.
Amid growing clamour for tighter curbs on people's movements to stem a rising tide of infections, the government has so far been reluctant to pull the trigger, warning of the heavy damage that could ensue in the world's third-biggest economy, already close to recession.
Instead, Prime Minister Shinzo Abe has urged school closures and called on citizens to avoid unnecessary and non-urgent gatherings and outings while preparing to roll out an economic stimulus plan next week - even as he acknowledged the country was barely avoiding a major jump in infections.
But the warning from the US Embassy in Tokyo to American citizens on Friday singled out Japan's lack of widespread testing so far and gave a sobering assessment of the potential strain on the health care system in a widespread outbreak.
"The Japanese Government's decision to not test broadly makes it difficult to accurately assess the COVID-19 prevalence rate," the Embassy said on its website, referring to the illness caused by the virus.
"While we have confidence in Japan's health care system today, we believe a significant increase in COVID-19 cases makes it difficult to predict how the system will be functioning in the coming weeks."
If US citizens wanted to return to the United States from Japan they should do so now, or risk remaining abroad for an "indefinite period", it said.
Japan has so far been spared the kind of explosive surge seen in parts of Europe, the United States and elsewhere, with about 3,000 cases and some 73 deaths so far. Globally, coronavirus cases surpassed 1 million on Thursday, while deaths have topped 50,000.
The comments from the Embassy came after Tokyo Governor Yuriko Koike said declaring a national state of coronavirus emergency would send a "strong message" that could help avoid an bigger outbreak, her most explicit nudge so far to the government.
That would give governors legal authority to ask people to stay home and businesses to close, but not to impose the kind of lockdowns seen in other countries. In most cases, there are no penalties for ignoring requests, although public compliance would likely increase with an emergency declaration.
Nobuhiko Okabe, director general of the Kawasaki City Institute for Public Health, said judging the timing for declaring a state of emergency was tough.
If issued too soon, it would have a big economic impact and have a serious effect on society, but if too late, the number of infected patients would rise, he said.
Tokyo has reported the highest number of infections in the country with nearly 800 infections - a tiny count compared with a core city population of nearly 14 million.
But experts are worried about the rise in the percentage of cases that can't be traced. As of end-March, the health ministry had counted 26 clusters of infections nationwide.
Asked what further steps would be taken in the capital if central government declared a state of emergency, Governor Koike said a Tokyo-style "lockdown" would entail asking people to refrain from holding events and the same kinds of pleas she was already making to residents.
These include working from home where possible and avoiding outings to bars and nightclubs - advice many have yet to heed, although coffee chain Starbucks and clothing retailer Uniqlo joined a string of other businesses in saying they would shutter dozens of stores this weekend.
The government on Friday told the hardest-hit regions to save hospital beds for severely ill patients, while keeping others with milder or no symptoms at home or in hotels. Until now Japan has been hospitalising all coronavirus patients, regardless of whether they are asymptomatic or have mild symptoms.
But beds are filling up in Tokyo and threaten to elsewhere, experts said this week.
Koike said Tokyo, for its part, would send people with light or no symptoms - the majority of the 628 hospitalised with the coronavirus as of Thursday - home or to hotels.
The capital was working with the government to secure accommodations, she said, while Prime Minister Abe has said utilising facilities that had been set up for the Summer Olympic Games - now postponed by a year - was under consideration.