SKOPJE, Macedonia — A freakishly violent rainstorm that Macedonia’s top weather official called a “water bomb” ravaged Skopje during the weekend, collapsing streets, inundating vehicles and drowning trapped motorists and homeowners, most of them caught by surprise.

At least 21 people were killed and 77 injured in what officials described on Sunday as the worst flooding disaster in a half-century to hit Skopje, the Macedonian capital and a city of more than a half-million people in the central part of the Balkan Peninsula.

Officials said the death toll could rise because many people were still missing after the storm, which hit with shocking ferocity on Saturday night.

The police, army units and firefighters rescued more than 1,000 people from the raging water that flooded streets, buildings, houses, clinics and schools. Traffic in much of the city was paralyzed.