A power blackout affecting large parts of Brazil has left millions of people stranded as underground railways, traffic lights, street lights and electric gates were hit.
Residents of the two largest cities, Sao Paulo and Rio de Janeiro, have been sending their accounts of the disruptions.
Bruno Jácome Üsler Janesch captured Rio de Janeiro in darkness
I've been living in the city of Sao Paulo for 15 years. I've never seen the city in complete darkness, as it was last night. I had just left my shop when the street lights started to blink for couple of seconds, then the whole city was plunged into darkness. As a result, the train service stopped, electric-powered buses stopped on the streets affecting the traffic and also the traffic lights weren't working leaving the city in a chaotic situation. People who were still in their offices were forced to get out of the buildings. One of my friends has kids on the 21st floor - he used a mobile phone to talk to them and comfort them as they were crying.
Marcelo Wong, Sao Paulo
The city is all dark. We can't connect to the internet, it is like living on an island. The only way we can learn anything about the situation is by using mobile phones or calling friends who live abroad. What would be the consequences if this happens during the World Cup or during the Olympics? It is total chaos!
Diego Vaz, in Cavalcanti, Rio de Janeiro
It happened without warning. I was in the shower and was really taken aback! It took around three hours for the power to be restored in my neighbourhood, but eventually we're back on track.
Felipe Silva, Sao Paulo
The lifts to our apartment are not working, the security gates to the apartment won't open so we had to try to find a hotel room. There were almost no rooms available. The roads are absolutely chaotic, taxis are driving without their 'for hire' sign. We just managed to get a cab and he explained that they're driving without their lights for fear of assaults. It's really scary - the city is pitch black. An already dangerous city has just become infinitely more dangerous.
Jeremy Holt, Sao Paulo
Power outages are quite common here in Rio de Janeiro, but usually for short periods of time. Since it happened at about 10pm, the worst part of it was trying to sleep at a temperature of about 30C without electricity.
Leandro Correia, Rio de Janeiro
It all began with dimming of the lights and it looked like a problem of power strength. Some lights here and there were normal, while others seemed to be in slow motion to power up. I was safe at home watching a movie, but because it happened late in the evening I wondered how thousands of people in the streets would be able to reach their homes. Shopping centres close at 10pm, and the chaos was shown on the internet with videos and photos posted. Soon the power was restored, which was around 3am. I think this is just a warning to what's coming next, not only in Brazil but globally. Cities such as Sao Paulo, Mexico City and Tokyo that are overpopulated will be the first to lose control over electric power and also water distribution.
Asael Silva, Sao Paulo
We were using mobile phones to find out what happened as there was no energy in the neighbourhood. It's crazy. Lights came on a while ago and I could hear people cheering but soon they went off again. My girlfriend who came back from work very late said that there were many accidents. We have had blackouts here before but never like this.
Ben W, Sao Paulo
Well, the lights are back on. Just as well as the recent heatwave ended today or we would have suffered more, but it had rained and cooled everyone down. It has to be said that Rio in a blackout is probably safer than Los Angeles or New York, as people seem phlegmatic and not in the least bit worried about a crime wave, so this doesn't seem to have affected people too much. Many people in my district, Laranjeiras in the south zone, took to the bars rather than climb the stairs home. So did I, but after 1am I finally decided to climb the 14 floors, luckily on what was quite a cool night, only to have the lights come on just as I was finishing my shower. It sounded like Brazil had scored a goal as the cheers resounded from every window. Just another night really, no dramatic news around these parts anyway. The story about Brazil goes on crime alert is pure invention - there's plenty of crime but probably not more last night than any other night.
Simon, Rio de Janeiro
I'm in Sao Paulo right now and almost all regions of the city are now back with power. The media is saying that many smaller hydro-electric and thermal power plants are now on full power to supply the needs of Sao Paulo state. There's still fear that these aren't going to solve the problem. In Rio, due to the lack of emergency situation planning, most regions are without power. Water pumping systems are also offline and will take 48 hours to be back on after the return of power.
Giordano M, Sao Paulo
At about 10.15 pm all the lamps in my apartment in Rio de Janeiro started to fade and glow at a very low intensity. They didn't immediately go out. I switched off the computer to avoid electrical damage. A few minutes later I looked out of my hilltop apartment windows at the usually brightly lit urban landscape that spreads out before me. Everything had gone dark, the whole city appeared to have been plunged into darkness.
Duncan Crossley, Rio de Janeiro
It was a pretty wild trip going through Sao Paulo which was almost pitch black but for the car lights. I was in the middle of mixing a song when the sound stopped and I was plunged into darkness. I glanced outside the window and saw that only cars were illuminating the city for as far as the eye could see. Back-up generators entered into action and some semblance of life crept back into Brazil's largest urban conglomeration - a city in post-reboot...
Phil Badiz, Sao Paulo
This was by far the worst blackout we've had in a decade. Short power failures are relatively normal even in Sao Paulo. Normally power returns in a couple of minutes, but this blackout lasted for nearly six hours. Luckily I got out of the lift about a minute before everything shut down. On a more positive note - at least we managed to have a romantic candlelight supper.
Patrick Schurt, Sao Paulo