Several Brazilian states, including three set to host June World Cup action, suffered power outages Tuesday, fueling fears over the country's ability to keep the lights on.
High demand combined with worries over supplies at a time of low rainfall led national grid operator ONS to warn of "disruption" in the integrated system as it noted outages in the north, southeast and south of the sprawling South American country.
Media reports suggested some three million people had seen supplies cut in 11 states, including Rio de Janeiro, and Parana in the south.
All three will welcome World Cup action in June.
The ONS said the cut lasted some 40 minutes before a gradual return to normal power levels.
The outage came a day after the grid registered record demand for energy, including a rush for air conditioning amid soaring temperatures in a sticky Southern Hemisphere summer.
The high demand came with water levels in reservoirs running low owing to low rainfall this year to date -- though authorities deny that is a factor.
The low water levels "have nothing to do with the demands of the system," mines and energy ministry executive secretary Marcio Zimmermann said.
Brazil has previously suffered a spate of similar problems.
Last August, eight northeastern states were left without power following a fire at an electrical station.
In October 2012, much of the north and northeast were plunged into darkness for hours owing to a national grid glitch, while a similar problem hit the capital Brasilia.
In late 2012, another outage left passengers at tourist-packed Rio's international airport groping in the dark.
President Dilma Rousseff blamed that incident on human error.
[Image via Agence France-Presse]