Updated

A widespread power outage hit at least eight states in northeastern Brazil on Wednesday, including four cities that will host matches during football's World Cup next year, authorities said.

About two hours after the outage, power was restored to all the state capitals, but smaller cities in the affected area were still without energy, according to the Electric Energy System Operator, which oversees power generation, transmission and distribution. A cause was not yet known.

The Brazilian government's electricity regulator, Aneel, said early reports indicated nearly all parts of the eight states were affected, which would mean tens of millions of consumers were involved. The power supply was reduced to just 10 percent of its normal level overall.

Officials were focusing on restoring the power before they turned their attention to figuring out the cause, an Aneel spokesman said on condition of anonymity, saying he wasn't yet authorized to discuss the situation.

Power outages used to be more frequent in Brazil and energy rationing was imposed for a time a decade ago. Improvements in infrastructure have been made in the energy sector, but major power outages still happen a few times a year.

Hydroelectric plants account for about 80 percent of the electricity generated in Brazil.

Earlier this year, reservoirs levels at hydroelectric dams in most of the country dropped to a third of their capacity because of a lack of rainfall. The levels were similar to those registered in 2001, when rationing was imposed and blackouts occurred with frequency.

Most regions have bounced back, but the reservoir levels in the northeast, in the midst of a severe drought, remain at just 38 percent of capacity, the worst region in Brazil.

The government has said that Brazil will not resort again to energy rationing because the country has thermal power plants that can be activated.

Brazil has an installed power generating capacity 121,000 megawatts, which the government says will be doubled over the next 10 years.

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Associated Press writer Marco Sibaja in Brasilia contributed to this report.