Tokyo's 31,878 new infections far outstripped a previous high in February, and many other regions also reported highs.
Thursday's national tally of 186,229 new infections was a record.
Despite few serious cases and deaths, officials warned hospitals were starting to feel the pressure from rising numbers.
"We need to keep a close eye on the infection situation, including the issue of access to medical services, with the highest vigilance," Chief Cabinet Secretary Hirokazu Matsuno told a regular news conference.
New COVID-19 infections nationwide were at their highest ever, he added.
Despite the surge, officials, including Prime Minister Fumio Kishida, have not called
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