TOKYO - The head of the government's coronavirus panel warned Wednesday that Japan has entered a "fourth wave" of infections, expressing a sense of crisis over the situation as highly contagious variants are spreading in several parts of the country.

Shigeru Omi, an infectious disease expert who chairs the government's subcommittee, said in parliament the government should expand areas subject to tougher anti-virus measures due to rising cases "in an extremely swift and nimble manner."

Prime Minister Yoshihide Suga, however, took a cautious stance as to whether the country has entered the new phase of infections, telling a House of Councillors plenary session, "I don't see a big wave (of infections) nationwide."

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Omi's warning came as the government is considering adding some prefectures to the list of areas requiring the quasi-state of emergency that involves shorter business hours for restaurants and bars, among other anti-virus steps.

The quasi-state of emergency is already in place in 6 prefectures including Tokyo and Osaka. The capital on Wednesday reported 591 new infections, while the western Japan prefecture reported a record 1,099 cases the previous day.

Yasutoshi Nishimura, minister in charge of the state coronavirus response, said the central government is working together with the Saitama and Aichi prefectural governments to beef up anti-virus measures, saying a recent surge in highly contagious virus variant cases in the 2 areas is worrisome.

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In a separate parliament committee meeting, Omi said, "It is necessary to fully consider the possibility of issuing a state of emergency" in Osaka, which entails stronger anti-virus measures such as closure of eateries and heavier punishments for noncompliance compared with the quasi-emergency.

Omi, a doctor and a former World Health Organization regional director for the Western Pacific, proposed the government play a leading role in supporting the strained medical system in the western Japan prefecture by sending staff from other areas.

Osaka Gov. Hirofumi Yoshimura has said he will consider asking the central government to declare a fresh state of emergency in his prefecture. The previous round was in place in Osaka from mid-January to late February.

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