A blackout left large parts of Brazil's north and northeast regions without any electricity Tuesday, and power disruptions were detected in the rest of the country, the National System Operator said.

At least 19 of Brazil's states were affected, according to a tally by online news site G1.

The outage affected public transportation. Passengers had to evacuate subway lines in major cities, including Sao Paulo, Belo Horizonte and Salvador. Traffic lights were out in other cities.

The blackout happened at 8:31 a.m. local time, government authorities said. Power was restored in some parts of the country by 10:00 a.m., the National System Operator said in a statement, but many areas remained without electricity.

The cause of the blackout was under investigation.