BBC News, Sao Paulo
Motorists found themselves driving through darkened streets
The lights flickered on and off and the popular soap opera showing on a TV screen in the corner suddenly vanished.
I was in a restaurant near my home in the heart of Sao Paulo when the power failure happened and along with dozens of other customers I suddenly found myself sitting almost in the dark.
It was not instantaneous - for quite a while the lights held a faint glow
At first I thought it was my neighbourhood which was affected - but I decided to head for home to check on whether my office computers had been damaged.
I had seen this kind of "virtual" power cut before when the electricity surges and then fades away again. Brazilians had told me forlornly of the damage this caused to TV sets and computers.
On the streets it was immediately obvious this was something more substantial. As far as I could see around me towering apartment blocks and busy streets were without light.
Some 10 Brazilian states were affected by the power loss
A nervous motorist pulled over to the side of the road to ask a passing pedestrian what had happened - even the normally aggressive Sao Paulo drivers seemed subdued.
It soon became clear - perhaps the only thing that was clear - that the scale of this blackout, which seems the right word, was breathtaking.
Major population areas were affected, with Rio de Janeiro, the proud winner of the 2016 Olympics, almost totally without light as well.
In fact, virtually the whole of the state of Sao Paulo was said to be in darkness - in other words, it affected some 40 million people or around 21% of the Brazilian population.
Subway trains halted
The blackout is said to have partially or totally affected at least 10 Brazilian states, and the geographical spread of the problem in this vast country was also amazing. One radio station estimated that at one stage 50 million people were without power.
Problems were reported from the city of Recife in the north-east of Brazil, to the southern tip of the country in the state of Rio Grande do Sul.
In Rio de Janeiro, subway passengers were reported to be walking along tracks to get to the nearest stations after metro systems ground to a halt.
Pedestrians were said to be negotiating their way around darkened streets using candles. Radio stations appealed to motorists to slow down and drive with care while extra police officers were on the streets to try to prevent opportunistic crime.
Transport bosses urged bus drivers to return to work so they could provide a more extensive service.
With the authorities searching for answers, the immediate focus of attention was the massive hydro-electric plant at Itaipu which provides 20% of Brazil's electricity.
But officials there insisted that the plant itself was working normally and suggested instead that the problem lay with a difficulty in the electricity transmission system.
The Brazilian Energy Minister, Edison Lobao, said there had been a strong storm near Itaipu when more than 17,000 megawatts of power was lost and he pointed to this as a possible reason for the power failure.
There was also renewed interest in a news story which emerged in the US this week claiming that computer hackers had disrupted the Brazilian power system in the past.
While nothing is certain, for the moment few people here are identifying this as a possible cause.
Officials began to talk of a "domino effect" to explain the vast spread of the power cuts.
In neighbouring Paraguay, virtually the whole country was said to be without light but for less than half an hour.
Power supplies have been a sensitive issue in Brazil ever since the apagao, or blackouts, of 2001 and 2002, which affected large parts of the country.
Power shortages then were made worse by a drought which had a severe impact on Brazil's extensive system of hydro-electric power.
The government of President Luiz Inacio Lula da Silva has always made it a priority to ensure this controversial episode in the country's history, which happened under a previous administration, was not repeated.
With the lights back on, ministers will be anxious to show that this latest massive power failure was not due to any mistake on their part.
Brazilians will also want to know why their country, which on so many fronts is racing ahead, was so drastically caught out on this occasion.