Tokyo is facing its first blackouts in nearly two decades as the city's main power company on Tuesday shut down the last of its 17 nuclear reactors for safety checks.
A series of accidents has knocked confidence in nuclear power
Tokyo Electric Power Company (Tepco) shut down its last running reactor in Fukushima, 200 kilometres (125 miles) north-east of Tokyo, at midnight (1500 GMT Monday).
Japan's nuclear industry been hit by a series of accidents and safety scandals in recent years - including the country's worst ever nuclear accident in 1999, when two people were killed because of lax safety standards.
The capital can switch to using fossil fuels to make up some of the shortfall. But unless Tepco completes the safety checks on several nuclear plants before the summer, Tokyo would face its first power cuts due to a shortfall in supply.
"Unless we can restart the facilities whose operations are halted now, we will inevitably face power shortages," said Cabinet spokesman Yasuo Fukuda.
"The government will do all it can," he added, although no date has been set for restarting the facilities.
Workers at Tokaimura had been illegally mixing uranium in buckets
"We don't know how long the inspection will last. At this moment, we don't know when to resume our operations," Tepco spokesman Mamoru Shirakashi said.
According to Mr Shirakashi, the company needs to run at least 10 nuclear reactors to meet its customer demands this summer, when air conditioner use peaks in Japan's humid season.
If this does not happen the company could rely on thermal power and buying power from other suppliers.
"But these measures are not enough to meet the expected energy demand," Mr Shirakashi warned.
Tepco was ordered to shut down its nuclear facilities for a full safety inspection after admitting last year it had covered up maintenance problems and obstructed government inspections.
The Japanese public is highly nervous about the safety of nuclear plants, especially since a radiation leak at a uranium processing facility in Tokaimura three years ago, which killed two and exposed 600 to radiation.
Afterwards it was discovered that workers at the power station had been illegally mixing uranium in buckets.