Chile suffered an unusual and extensive electricity blackout Tuesday that forced the evacuation of the Santiago metro, the Senapred disaster service said.

Initial reports said the outage started at 3:16 pm (1816 GMT) and stretched all the way from Arica in the north of the long, narrow South American country to Los Lagos in the south, the agency reported.

No reason has been given for the failure in the country of 20 million people in the middle of the southern hemisphere summer.

Chile boasts one of the best power networks in the region, and has not had a blackout this big in about 15 years.

In the capital of seven million inhabitants, hundreds of people were evacuated from the metro. 

"They let us leave work because of the power cut, but now I don't know how we will get home because all the buses are full," worker Maria Angelica Roman, 45, told AFP in Santiago.

"Our teams are deployed at all stations to support safe evacuations. Once this process is completed, the stations will remain closed until power is restored," the metro company said in a statement.

In 2010, damage to a power plant in southern Chile plunged hundreds of thousands of people into darkness for several hours.