French President Emmanuel Macron announced a month-long extension of the country’s nationwide lockdown, prolonging measures to fight the new coronavirus into mid-May, as Italy and Spain—two of the nations hit hardest by the pandemic—signal that drastic restrictions on their populations also would continue as the spread of the virus slows.

Mr. Macron extended France’s lockdown, which began nearly a month ago, until at least May 11. After that date, he said in a national address Monday, “as many workers as possible” could begin…