The bill, which is yet to be approved by parliament, will see the creation of a body to handle claims made against TEPCO and will be funded by public money as well as contributions from power companies.

Shares in the utility soared 18.59 per cent after the bill was approved.

The government-devised aid plan for TEPCO will include the purchase of its corporate bonds, stocks and assets to support the company's operations, but analysts warned that uncertainty still surrounded the bill.

"Investors are buying back TEPCO shares believing that the government will pay a decent price for shares, but nothing concrete is known yet and it's too soon to make that assumption," Akino told Dow Jones Newswires.