Japan expanded its COVID-19 vaccine rollout beyond the Tokyo metropolitan area on Thursday, with health workers set to be inoculated at 100 hospitals across the country by next week.

Prime Minister Yoshihide Suga inspected the program at the Tokyo Medical Center, the first institution to begin administering Pfizer Inc.'s vaccine the previous day.

"I felt that health workers are placing much hope on vaccinations," he said after speaking with staff at the state-run hospital. "I hope to deliver vaccines to people nationwide as soon as possible."

Prime Minister Yoshihide Suga watches a person being vaccinated at Tokyo Medical Center on Feb. 18, 2021. (Kyodo)

Hospitals in Ibaraki, Nagano and Okayama were set to begin vaccinations on Thursday as the country seeks to inoculate an initial group of 40,000 health workers before expanding to other parts of the population.

No severe side effects were reported Wednesday among the 125 people inoculated at eight hospitals in the Tokyo metropolitan area. The Tokyo Medical Center said it plans to give shots to about 60 people per day and complete vaccinations of 800 individuals by the end of March.

Of the initial group of 40,000 health workers, 20,000 are taking part in a study of potential side effects caused by the vaccine, with data gathered by the health ministry's research team due to be released every week.

The participants are being asked to keep daily records for seven weeks after receiving the first of two shots. The shots will be administered three weeks apart.

Vaccination of a further 3.7 million front-line health care providers is to begin in March, followed by 36 million people aged 65 or older from April, according to the country's vaccination timetable.

People with pre-existing conditions and those working at elderly care facilities will be next in line, followed by the general population.

Japan trails about 80 countries in starting its coronavirus vaccination rollout, as the country requires additional clinical trials on its own population to ensure safety before approving the vaccines.