Swathes of Japan are being plunged into darkness amid rolling blackouts.
The drastic action to conserve electricity was ordered by the government in the wake of the devastating earthquake and tsunami which crippled several nuclear reactors.
The resource-poor country depends on nuclear energy for about a quarter of its electricity. Out of Japan's 54 reactors, 11 are closed.
With the quake-stricken Fukushima Daiichi plant lost to the national power grid, there is a power shortfall of 10 million kilowatts, according to the economy, trade and industry minister.
The rationing is expected to last weeks rather than days, affecting millions of people from the northeast coast down to Shizuoka, 200km south of Tokyo.
Prime Minister Naoto Kan has acknowledged the difficulties the enforced blackouts will bring, including disruption to gas and water supplies and medical treatment.
"This was a hard decision to make, knowing that it would cause a lot of inconvenience to the public. Please be creative in protecting yourselves from this blackout," he said announcing the cuts on Sunday.
As they began, roads leading into central Tokyo were snarled with traffic as a result of limited rail services.
Some ATMs will not function during outages; local media said if traffic lights were affected policemen would be deployed.
One resident in Kanagawa prefecture, south of Tokyo, told the BBC there was "a sense of quiet panic" as almost all petrol stations had sold out of fuel and the few shops that were open were out of basic food and bottled water.
Major vehicle manufactures have halted production across Japan. Toyota has announced that its factories will remain shut until Thursday at least, Honda until 20 March.
Several other high-profile companies - Toshiba, Sony, Nippon Paper Group, for example - have closed plants due to outages and the need for checks.
In one concession, officials said central Tokyo would be spared from power cuts, as central government offices and many company headquarters are housed there.
Many parts of the world cope regularly with power disruption, and rolling blackouts are a common practice, says Charles Ebinger, director of energy security at Brookings Institution.
"It's effectively rationalising the remaining power as an alternative to having the whole system trip and come crashing down," he says.
In a situation of this magnitude, Mr Ebinger says, the utility company will go to its top 25 to 30 commercial and industrial customers and ask who has the capacity to cut back on its energy usage - so the cuts are made on a voluntary rather than blanket basis.
"Residential customers will take a hit - typically they will have signed a deal with the utility company to allow for cuts in exchange for a lower charge rate - but the burden usually falls on the big, energy-intensive businesses," he says.
In the dark
Residents are, however, trying to do their bit.
In an apparent show of solidarity, residents cut back on their electricity usage enough for the Tokyo Electric Power Company (Tepco) to scale back its initial blackout scenario.
Hiroka Shoji lives with her family in Chiba prefecture, close to Tokyo Disneyland.
"I feel blessed that we weren't in a place directly affected by the quake and tsunami. I'm sure those feelings are one big reason why people have cut back so much voluntarily on their electricity use."
Her family has moved into one room to try to reduce electricity consumption.
She has stockpiled extra batteries and food, and the bath has been filled with water so the family will be able to flush the toilet in preparation.
She says her biggest challenge is getting to work in central Tokyo.
"There is a 30-50% decrease in the trains running and they are stopping more frequently to save power. I had to stay at home yesterday because of the disruption. Today there was a lot of waiting around and huge crowds at stations."
In the longer term, Japan will have to import more conventional resources such as oil, fuel and natural gas to make up for the shortfall in electricity generation.
After explosions at three of its reactors, the Fukushima Daiichi nuclear plant will almost certainly be decommissioned.
"The Japanese are already buying LNG (liquefied natural gas) - cargos are being diverted from Europe where some countries have a supply glut," says Mr Ebinger.
Russia has said it is willing to divert 6,000 MW of electricity to help Japan, and its natural gas giant Gazprom is also preparing to send 200,000 tonnes of LNG to Japan in April and May, officials said.
But for those living with the blackouts, with sketchy information from the authorities and a nuclear crisis unfolding by the day, many feel very much in the dark.