Japan is facing what some are calling its sixth wave of coronavirus infections with cases in some places at their highest in months. One official has blamed US military personnel for spreading the Omicron variant.
US Forces Japan said that due to an increase in COVID-19 cases at US installations and throughout Japan it was establishing more stringent mitigation measures including requiring US military personnel to wear masks off base and for stricter testing.
"The mitigation measures we have instituted ... are intended to protect our force's readiness, the well-being of our families, and the health of Japan's citizens," the force said in a release.
"We recognise we all have a part to play in keeping our communities safe."
There are more than 100,000 US service members, dependents and contractors in Japan.
Earlier, Foreign Minister Yoshimasa Hayashi asked US Secretary of State Antony Blinken for US service members to be restricted to their bases, Chief Cabinet Secretary Hirokazu Matsuno told reporters.
Matsuno said Japan was "gravely concerned" about COVID infections at US bases.
The southern prefecture of Okinawa, host to 70 per cent of US military facilities in Japan, is at the epicentre of Japan's latest surge of cases and it asked the central government on Thursday to impose new restrictions, known as quasi-emergency measures, which would likely include limiting the opening hours of restaurants and bars.
Announcing the request, Okinawa Governor Denny Tamaki said new cases there were expected to surge to 980 on Thursday from 623 the day before.
Tamaki told reporters this week he was "furious" about what he called inadequate infection controls at US bases that allowed the Omicron variant to spread to the public.
The western prefecture of Hiroshima announced it would also request quasi-emergency measures. Various levels of emergency controls had been in place over most of Japan last year until their lifting on September 30.
Japan halted the entry of almost all foreign travellers in late November after the World Health Organisation listed Omicron as a variant of concern.
But the US military moves staff in and out under a separate testing and quarantine regime.
A US Marine Corps station in the prefecture of Yamaguchi, in western Japan, said it discovered 115 new cases on Wednesday, after 182 the previous day.
