Electricity services have been restored to more than 50% of Argentina and Uruguay following a massive blackout that left around 48 million people without power, authorities said.

At around 3:30pm (1830 GMT), Argentina's Energy Minister Gustavo Lopetegui said services had been restored in 56% of the country.

In neighboring Uruguay, the state power company UTE said power had returned to three-quarters of the country.

The cut, which happened just after 7am, also affected Paraguay, which reported short, localized losses of power.

A massive outage had blacked out all of Argentina and Uruguay, leaving both South American countries without electricity, power companies have said.

Uruguay's system went down at 7.06am, according to the Uruguayan power company UTE, which attributed the outage to "a fault in the Argentine network."

Two Argentine power companies confirmed the failure knocked out electricity throughout Argentina, without specifying the cause.

"A massive failure in the electrical interconnection system left all Argentina and Uruguay without power," Edesur Argentina said on Twitter.

Edenor, Argentina's largest electricity distributor, attributed the outage to a "general failure in the interconnection system."

UTE said the failure left Uruguay's "entire national territory without service, as well as several provinces of the neighbor country."

More than an hour after the blackout, UTE said its system was being brought back "from zero."

"Some coastal cities already have service and work continues toward general restoration (of power)," it said.