A rare blackout hit the entire Dominican Republic on Tuesday, snarling traffic and paralyzing businesses in the country of nearly 11 million people.

Officials blamed a failure in the grid’s transmission system, although it wasn’t immediately clear what caused it.

Generation units in San Pedro de Macorís and the Quisqueya Power Plant shut down, triggering a cascade of failures at other transmission and generation plants, according to the Dominican Electricity Transmission Company, a decentralized state agency.