A massive blackout hit the southern half of Brazil late Tuesday, plunging tens of millions of people into darkness and triggering a crime alert. Airport operations were hindered, and subways ground to a halt. Power was largely restored to much of southern Brazil early Wednesday.

The blackout hit at 10:20 p.m. local time. According to an AP report, power was out for more than two hours in Rio de Janeiro, Sao Paulo and several other major cities, affecting millions of people.

Reports have differed on whether capital city Brasilia lost power and on how long the outage lasted. All of Paraguay also experienced a brief blackout.

The government has confirmed that the power failure started with the Itaipu dam, the world's second biggest hydroelectric producer, which supplies 20 percent of Brazil's electricity. Brazilian authorities blamed storms that took down power lines and towers, causing a domino effect that rippled across the region, an AP report said.

The Itaipu dam straddling the Brazilian-Paraguay border stopped producing 17,000 MW of power, Brazilian Mines and Energy Minister Edison Lobao said. He said outages hit nine of the 27 states.