Japan is set to expand emergency restrictions to eight more prefectures to fight a surge in Covid-19 cases, as worries deepen about strains on the nation's medical system in Olympics host Tokyo and around the country.

Coronavirus infections are surging faster than ever before as new cases hit record highs in Tokyo, overshadowing the July 23-Aug 8 Olympics and fuelling doubts over Prime Minister Yoshihide Suga's handling of the pandemic.

"New infections are rising at an unprecedentedly fast pace," Economy Minister Yasutoshi Nishimura told a panel of experts at which he made the new proposal.

"The situation on the ground [at hospitals] is extremely severe," Nishimura added, noting that serious cases had doubled in the past two weeks.

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