Chilean authorities said they had restored power to most homes on Wednesday, hours after a massive, rare blackout caused transport chaos in the capital and forced the president to declare a state of emergency and curfew across much of the country.

Chile's worst blackout in well over a decade struck on Tuesday afternoon, leaving millions without power.

President Gabriel Boric blamed private companies that manage the grid for the system's failure.

"This is outrageous! The daily life of millions of Chileans can't be impacted like this by companies that don't do their job," Boric said in a statement issued by his office.

Early Wednesday, "90 percent of (electricity) consumption was restored" to homes, the power system's operator said in a statement.

According to the Senapred disaster response agency, the outage affected an area stretching all the way from Arica in the long, narrow South American country's north to Los Lagos in the south -- an area home to over 90 percent of Chile's 20 million people.

The blackout disrupted transport in the capital Santiago, where thousands were evacuated from the metro and people jostled to board overflowing buses.

President Boric had activated "a state of emergency due to a catastrophe" and announced a curfew until 6am Wednesday.

Interior Minister Carolina Toha ruled out sabotage as the reason for the power loss, which began at 3.16pm in the middle of the southern hemisphere summer.

"There is no reason to assume that this is an attack," she said on Tuesday, telling reporters it was more likely "a failure in the system's operation".

The metro company, which transports 2.3 million passengers every day, said workers were deployed to all stations "to support safe evacuations."

Out-of-service traffic lights caused major gridlock, with some people having to walk for hours under a hot sun to reach their homes. (AFP)