The operator of Japan's crippled Fukushima nuclear plant said Wednesday it booked a $4.3 billion annual net profit owing to an electricity rate hike and a massive government bailout following the 2011 disaster.

Tokyo Electric Power (TEPCO) was teetering on the brink as cleanup and compensation costs stoked huge losses and threatened to collapse the sprawling utility until Tokyo stepped with a multi-billion dollar rescue.

The company at the centre of the worst nuclear accident in a generation said it earned 438.65 billion yen ($4.3 billion) in the fiscal year to March, compared with a net loss of 685.3 billion yen in the same period a year earlier.

Sales rose 11.0 percent to 6.63 trillion yen, it said.

The company's results got a boost from a rate hike, and helped offset a decline in the amount of electricity TEPCO sold owing to warmer-than-usual winter weather, it said.

It also booked a special gain of 1.8 trillion yen based on funds the company received from a government-backed bailout fund as well as asset sales.

But it added that rising fossil fuel costs after Japan switched off its nuclear reactors were pressuring its bottom line.

"The business environment that surrounds us remains very serious," TEPCO president Naomi Hirose told a news conference.

The Fukushima plant's cooling systems were swamped by the 2011 tsunami, sparking reactor meltdowns and radiation leaks.

Tens of thousands of people were evacuated from around the plant with decommissioning of the site expected to take decades.