Japanese electricity companies said Friday they had booked multi-billion dollar losses in the last year after the Fukushima disaster shuttered nuclear power plants and ramped up fossil fuel use.

Kansai Electric Power said it incurred a net loss of 242.26 billion yen ($3 billion) turning around from a year-before profit of 123.14 billion yen.

Operating loss came to 229.39 billion yen, despite the fact that revenue had inched up 1.5 percent to 2.81 trillion yen.

"Operating costs surged from the year before with the lower utilisation rate of nuclear power plants and higher fuel prices pushing up costs of thermal power generation and of electricity purchases from other companies," it said.

All but one of Japan's nuclear reactors are offline amid a lingering public distrust of the technology after last year's tsunami-sparked crisis at Fukushima.

Japanese power companies have warned a hot summer could bring blackouts for some areas unless nuclear plants are re-started. The shortfall is expected to be particularly severe in western Japan, the region partially served by Kansai Electric Power.

Hokkaido Electric Power, which until it flicks the switch on May 5 is the only company with a reactor still working, reported a net loss of 72.07 billion yen, reversing a profit of 11.98 billion yen in the previous year.

Tohoku Electric Power, based in the nation's northeast devastated in the March 2011 earthquake and tsunami, said its net loss grew to 231.91 billion yen in the year to March 2012 from 33.71 billion yen in the previous year.

Tokyo Electric Power, the operator of the crippled Fukushima Daiichi plant, is struggling to rehabilitate itself with government assistance.