More than 50 percent of Japan's population has been fully vaccinated against COVID-19, government data showed Monday, with the inoculation rate finally catching up with countries such as the United States after a slow start marred by vaccine supply shortages.

Of the nation's population of 125 million, about 64 million people, or 50.9 percent, had received two doses of a COVID-19 vaccine as of Monday, after the inoculation program was launched in February initially for health care workers and expanded to the elderly and later to other members of the public.

Over 60 percent of the population is expected to be fully vaccinated by the end of September, bringing Japan on par with major European countries such as Britain and France, according to the government.

The announcement of the latest vaccination rate came as the government on Monday extended the coronavirus state of emergency in Tokyo and 18 other prefectures through Sept. 30 as hospitals remain stretched. The emergency was originally slated to end the previous day.

Japan initially lagged far behind other major economies in inoculating its population. Facing criticism, the government has made relatively fast progress since, setting up mass inoculation sites and offering workplace vaccinations.

"This is the result of our cooperation and close collaboration with local governments and health care workers," said Katsunobu Kato, the top government spokesman, at a press conference Monday.

In the United States, 53.8 percent of the population had been fully vaccinated as of Sunday, according to Centers for Disease Control and Prevention data.

The Japanese government has been accelerating inoculations of younger people, as it aims to finish vaccinating all eligible people who wish to receive shots by November.

While Japan's health care system remains under strain due to the highly contagious Delta variant of the coronavirus, the government plans to relax curbs on traveling and large events from around November once most of the population has been fully vaccinated.

While hospitals continue to struggle, the daily infection count has been trending downward.

The Tokyo metropolitan government on Monday reported 611 new cases, bringing the seven-day rolling average to 1,333 per day, down about 50 percent from the previous week.

Nationwide, the number of new infections totaled 4,171, falling below 5,000 for the first time in over a month.