Buenos Aires, Jun 17 (IANS): Electricity was restored across Argentina after a massive power outage due to an electrical grid failure led to a historic blackout in the country.

The outage started shortly after 7 a.m. on Sunday, a day marked by heavy rains. It was not until three hours after it was reported that the situation began normalizing in the country, and at 9.35 p.m. all of the supply had been restored, reports Efe news.

The sudden power outage, which also affected Uruguay and parts of Paraguay, led to the suspension of train and metro services in Buenos Aires, although major airports were operational.

The blackout also affected the distribution of drinking water, which led the company in charge of the water supply in Buenos Aires and its populous urban belt - which brings together 13 of the 40 million people living in Argentina - to urge users to ration their consumption at home.

An emergency plan was activated for hospitals in the capital city to ensure care of patients, with generators in intensive care areas and operating rooms.

In Twitter messages posted seven hours after the start of the blackout, President Mauricio Macri said what happened was unprecedented and that it would be thoroughly investigated.

Energy Secretary Gustavo Lopetegui convened a press conference in which he said the blackout was "very serious" and cannot happen again.

According to the official explanation, the power grid failure was caused by a collapse of the Argentine Interconnection System (SADI), in particular an electricity transport connection in the northeast of the country near the border between hydroelectric power plants Yacyreta (Argentine-Paraguayan project) and Salto Grande (Argentine-Uruguayan).

Over the next 48 hours, electricity distribution companies will be required to submit a preliminary report on what happened and a full report within 10 days, and those found responsible will be subject to sanctions as according to law.

In particular, the provinces of Santa Fe, San Luis and Formosa were affected, where regional elections were held amid reports of problems with lighting polling stations early Sunday.

In the southernmost province of Tierra del Fuego, located on the island of the same name, elections were also held. It was the only one with electricity as it did not depend on SADI for its power supply.