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 actually caused the disruption that pushed much of the country's power grid into shutdown, from the northernmost Chilean port of Arica to the southern Los Lagos agricultural region.

Chile's national disaster response service, Senapred, reported that a "disruption in the supply of electricity" had provoked a "massive power outage" across 14 of the country's 16 regions, including Santiago, a city of some 8.4 million people, where authorities said there would be no subway service until further notice.

Interior Minister Carolina Toha said hospitals, prisons and government buildings were switching on backup generators to keep essential equipment operating.

In a press conference, Toha urged the public to stay calm and said officials were racing to put the grid back in operation and restore electric service across the country of some 19 million people.

"It's affecting the entire electrical system of the country," she said of the breakdown in the 500-kV backbone transmission line.

Toha said if all areas didn't return to normal by sunset, the government would take emergency measures to avert a crisis.

One of the country's main electricity distributors, Saesa, which serves more than 1 million people across Chile, confirmed that all of its customers had experienced the power failure.

Officials said they were evacuating passengers from darkened tunnels and subway stations in Santiago and elsewhere in the country, including the coastal tourist hot spot of Valparaiso.

Videos on social media from all over Chile, a long ribbon of a country stretching 4,300 kilometers (more than 2,600 miles) along the southern Pacific coast, showed chaos at intersections with no functioning traffic lights, people having to use their mobile phones as flashlights in the underground metro and police dispatched to help evacuate office buildings.

Transport Minister Juan Carlos Munoz urged people to stay home, saying it's "not a good time to go out since we have a transport system that is not operating normally." At the very most, he said, just 27% of city traffic lights are working.

Mobile phone services also blinkered offline in parts of the country. Authorities at Santiago International Airport said terminals had switched to emergency power to keep flights operating as usual.