Even by the standards of crisis-weary Venezuelans, the blackout -- which began late Thursday -- was one of the longest and most widespread in memory, heightening tensions in Maduro's power struggle with his US-backed rival, opposition leader Juan Guaido.

Maduro made the decision to shut down offices and schools "in order to facilitate efforts for the recovery of electricity service in the country," Vice President Delcy Rodriguez tweeted.

Power supply was gradually being restored to large areas of Caracas on Friday afternoon, as the country slowly began to emerge from the 24-hour blackout.

Electricity supply was also being resumed in areas of Miranda state and Vargas, which contains the country's international airport and main port.

Other areas like the western states of Zulia, Tachira and Barinas -- where lengthy outages are common -- were still without power.

Defense Minister Vladimir Padrino, patrolling the west of the capital Caracas in an open-topped military jeep, said "everything is calm throughout national territory" as electricity workers tried to restore the electricity.

-'Total madness'-

The outage had left most of the country in chaos, crippling day-to-day functioning of hospitals and other public services, according to local press reports.

Witnesses described scenes of chaos at several hospitals as people tried to move sick relatives in the dark to clinics with better emergency power facilities.

Marielsi Aray, a patient at the University Hospital in Caracas, died after her respirator stopped working.

"The doctors tried to help her by pumping manually, they did everything they could, but with no electricity, what where they to do?" asked Jose Lugo, her distraught uncle.

Generators at the JM de Rios children's hospital in downtown Caracas failed to kick-in when the blackout hit, said Gilbert Altuvez, whose eight-year old boy is among the patients.

"The night was terrible. Without light. Total madness," he said.

Emilse Arellano said urgent dialysis for her child had to be cancelled Friday, after a night where staff worked in the light of cellphones.

"The children were very scared."

The putrid odor of rotting flesh hung around the entrance to Caracas' main Bello Monte morgue on Friday where refrigerators had stopped working and worried relatives gathered outside, waiting to be allowed to bury their dead.

Guaido, speaking to supporters at an gathering marking International Women's Day, confirmed that power "is beginning to come back in some sectors."

"It can't be normal that 50 percent of hospitals in the country don't have an electric plant," he said.

- 'Electrical war' -

The blackout in the capital was total and hit at 4:50 pm (2050 GMT), just before nightfall on Thursday.

Traffic lights went out and the subway system ground to a halt, triggering gridlock in the streets and huge streams of angry people trekking long distances to get home from work.

Thousands of homes in Caracas -- a crime-ridden city of two million people -- were without water supplies.

Telephone services and access to the internet were also knocked out.

The capital's Simon Bolivar international airport was hit, as were others across the country.

Following Maduro's decision to close the borders to keep out humanitarian aid for his people, the country was completely isolated Friday.

"The electrical war announced and directed by US imperialism against our people will be defeated," Maduro tweeted.

"Nothing and no one can defeat the people of Bolivar and Chavez," Maduro said, referring to the liberation hero Simon Bolivar and Maduro's predecessor and former boss, the late socialist icon Hugo Chavez.

Guaido, meanwhile reiterated his call for mass protests on Saturday.

"All Venezuela, now with more force than ever, returns to the streets of the whole country, we return to the streets and we won't go out until we reach the goal," he said.

- 'Tired, exhausted' -

Venezuelans are wearily accustomed to blackouts. They have been common in the west of the oil-rich country for years, but have eventually spread to Caracas and other areas.

Critics blame the government for failing to invest in maintaining the electrical grid, although the government often blames external factors when the lights go out.

The state power company Corpoelec said there has been sabotage at the Guri hydroelectric plant in Bolivar state, one of the largest in Latin America. It gave no details.

Maduro is struggling in the confrontation with Guaido, who has declared himself interim president and is now backed by some 50 countries led by the United States.

Guaido says Maduro's rule is illegitimate, arguing that his re-election win last year was fraudulent. He wants Maduro to resign from the Miraflores Palace and make way for new elections.

US Secretary of State Mike Pompeo said Maduro is wrong to blame the US or any other country for Venezuela's woes.

"Power shortages and starvation are the result of the Maduro regime's incompetence," he tweeted.