SANTIAGO, Chile — A sweeping blackout hit Chile on Tuesday, stranding commuters, knocking out traffic lights, paralyzing countless businesses and leaving millions of people across the South American nation without power.

The National Electrical Coordinator, Chile’s grid operator, said a disruption had occurred in a high-voltage transmission line that carries power from the Atacama Desert of northern Chile to the capital of Santiago in the country’s central valley.

It did not say what…