The mayor's daughter had earlier reported him missing. Local media reports said he left his house wearing a black hat and a backpack.
The United States has repeatedly called for China to participate in negotiations to extend a flagship nuclear arms treaty between the US and Russia that is due to expire in February next year.
Across the country, about 3.6 million people were advised to evacuate amid the coronavirus pandemic. Residents have been urged to seek shelter with friends or relatives if possible to avoid overcrowding evacuation centres.
China, where the new coronavirus is thought to have originated, brings state, military and private sectors together in a quest to combat a disease that has killed over 500,000 people worldwide.
Hong Kong leader Carrie Lam hailed the opening as "a historic moment" and said China's intelligence apparatus would be an "important partner" in helping to safeguard national security.
Senior North Korean foreign ministry official Kwon Jong Gun ridiculed “nonsensical” calls by South Korea for revived negotiations between the US and North Korea, saying it has lost its relevance as a mediator.
TikTok to exit Hong Kong market within days, while other technology companies, including Facebook, WhatsApp, Telegram, Google, Zoom and Twitter, suspend processing government requests for user data in the region over Beijing's new security laws.
Twitter said it had suspended all information requests from Hong Kong authorities immediately after the law went into effect last week.
Last week, China enacted a security law outlawing four national security crimes: subversion, secession, terrorism and colluding with foreign forces.
Helicopters and boats have rescued more people from their homes in the Kumamoto region. More than 40,000 defense troops, the coast guard and fire brigades have been taking part in the operation.
Hong Kong public libraries have placed certain books under review to see whether they "violate the stipulations" of a new national security law that China imposed on the financial hub.
Saturday's unprecedented rains in the Kumamoto prefecture of central Kyushu unleashed floods and landslides.
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