Venezuela’s embattled president, Nicolás Maduro, has been forced to close schools and give workers the day off after a severe and potentially destabilizing blackout dragged into a second day.

On Friday morning, more than 19 hours after power failed across most of the country, Venezuela’s vice-president, Delcy Rodríguez, announced that schools would not open and private- and public-sector workers should stay at home.

Rodríguez told the state-run broadcaster Telesur her country had fallen victim to “an act of electric sabotage committed by Venezuela’s extreme-right opposition” on a hydroelectric plant in the country’s south.

The streets of Venezuela’s capital, Caracas, were quiet amid growing fears over the human cost of what observers called the worst power outage in memory.

“I can’t even imagine how the children who are in neo-natal intensive care units spent the night – the ones who are connected to ventilators,” said Eunice Lample, a paediatrician at one such practice in Caracas.

“The first thing I thought when I woke up this morning was: ‘How many people died overnight? … because of the ineptitude of this usurping government,” the 60-year-old doctor added. “The country has stopped.”

Harrowing video footage posted on social media showed doctors trying to keep children breathing at the Supreme Commander Hugo Chávez paediatric hospital in Caracas.

At one of the city’s maternity wards an Associated Press reporter saw crying mothers watch nurses use candles to monitor the vital signs of their premature babies after backup generators shut off.

A prominent Telesur reporter with close government ties blamed “a technological and cyber attack” on the Guri hydroelectric plant.

People get on a bus during the blackout. Photograph: Reuters

Rodríguez denounced the incident as part of “a perverse plan” to overthrow Maduro, who is facing a struggle to retain power after opposition leader Juan Guaidó declared himself Venezuela’s rightful interim leader on 23 January and was recognized by most western governments.

Rodríguez also alleged the United States – Guaidó’s key international backer – had played some role in the incident, particularly the “putrid hands” of the Republican senator Marco Rubio, a vocal cheerleader for those trying to force Maduro from power.

Rubio reacted to those claims with sarcasm. “My apologies to people of Venezuela. I must have pressed the wrong thing on the ‘electronic attack’ app I downloaded from Apple. My bad,” he tweeted.

Maduro opponents rubbished suggestions the outage was the result of an anti-government conspiracy.

“Guri has collapsed because of a lack of maintenance, just like the thermoelectric plants and the transmission and distribution lines,” tweeted Hugo Chávez’s former oil minister, Rafael Ramírez, who went into exile after splitting with Maduro in 2017.

“It is the incapacity and the indolence of this government that have led us to this total collapse.”

Giancarlo Fiorella, the editor of the In Venezuela blog, said the government routinely blamed political foes for such increasingly common failures.

“But they’ve never come close to providing any kind of evidence. It is much more likely that this is one of the symptoms of an electrical system that we know has been in crisis for at least a decade.”

Fiorella said the power crisis was the result of “neglect, disrepair and corruption at the highest levels of the Venezuelan government – precisely the same things that are leading to the crisis in the healthcare sector, the economic crisis. This is one of the facets of the Venezuelan crisis”.

A couple walks along a street in darkness. Photograph: Yuri Cortéz/AFP/Getty Images

Local newspapers said the blackout began at about 4.52pm on Thursday and affected nearly all of Venezuela’s 23 states.

Flights in and out of Venezuela’s decaying airports were suspended and workers were forced to hike home after the Caracas metro ground to a halt.

On Friday morning power had still not been restored to large swaths of the country.

Maduro had called a series of “anti-imperialist” marches on Saturday designed to shore up his rule but it was unclear if they would still go ahead.

Fiorella predicted the outage – which he called the longest in living memory – would have both a political and a human cost.

“It is almost guaranteed at this point that people have died as a result of this. I would be extremely surprised if all the hospitals in the country had enough diesel to run their generators at all, [let alone] for 16 or 17 hours,” he said.

The power cut would also “add fuel to the fire” of an already volatile political situation. He said: “This is certainly not good for Maduro if he’s trying to seem like he is in control of the situation.”

International flights in and out of Caracas were delayed or cancelled and a late-night flight from Bogotá was reportedly forced to abort its landing approach and return to Colombia.

At Bogotá’s El Dorado airport, would-be passengers grew impatient and frustrated as staff announced that their flight to Caracas would be delayed by at least nine hours.

“I’ve never heard of a power cut this big and lasting this long,” said one Venezuelan traveller. “Every time I go back home it gets worse, but what can we do? This is the country we have.”

Venezuela’s land and maritime borders were closed following last month’s humanitarian aid showdown, and with air travel now crippled, the country is effectively locked down.