Japan is declaring a state of emergency in three more prefectures hit hard by the Covid-19 pandemic, it said on Friday, in a surprise move that reflects growing concern about the spread of the coronavirus.

The latest declaration comes as Japan grapples with a surge of a more infectious virus strain just 10 weeks before the Tokyo Olympics are due to start on July 23.

Hokkaido, Okayama and Hiroshima will join Tokyo, Osaka and four other prefectures on Sunday under a state of emergency until May 31, said Economy Minister Yasutoshi Nishimura, who is also in charge of virus countermeasures.

With an eye on the economy, the government had originally proposed a more targeted "quasi-emergency" declaration for...