A major power outage crippled several of Argentina's provinces on Wednesday, including parts of Buenos Aires, plunging millions of people into darkness for at least two hours as summer temperatures soared, officials said.

In the capital, the lights flickered back on at about 6:00 pm (2100 GMT) in the metro system, and public services were gradually restored.

Reports of the first outages came in from 4:00-5:00 pm, with traffic lights out of order and Buenos Aires metro stations in total darkness.

Argentina's undersecretary for energy Santiago Yanotti told the C5N network that power demand had soared due to the high temperatures. In Buenos Aires, it was 36 degrees Celsius (97 degrees Fahrenheit) on Wednesday.

The power cut is believed to have been caused by a fire in a field near high-tension lines connected to the Atucha 1 nuclear power plant, Yanotti said.

The plant was taken offline as a safety precaution, sparking the widespread problems nationwide, the country's national nuclear power authority Nucleoelectrica said.

There was no immediate official data on the numbers of households affected, but a government source told AFP that Cordoba, Santa Fe and Mendoza provinces along with Buenos Aires experienced outages.