Naoki Sunoda, a spokesman for the utility, said workers are trying to determine the safest way to proceed in battling to prevent a meltdown of the damaged reactors.
Up to 600 technicians, firefighters and soldiers are working at the plant day and night, in spite of the radiation risk.
"Radiation levels are high, but nothing will be resolved if we stay away," Sunoda told reporters. "Our objective is to restore power to all reactors so cooling functions can be restored."
On Thursday, two workers were burned after they waded into highly radioactive water inside the plant's No. 3 reactor.
A masked survivor walks in the devastated city of Kesennuma on Sunday. (Yu/AP)
Engineers are pumping fresh water onto the plant to try to keep fuel rods inside the reactor cores and pools from being exposed to the air.
Evidence of the worsening conditions were shown in radioactive iodine levels of 1,150 times the legal limit in seawater about 1,000 feet offshore from the facility, causing new concerns about seafood contamination.
Japanese government spokesman Yukio Edano revealed Sunday that workers were also testing the areas around the plant's six reactors for the presence of leaked plutonium.
Sakae Muto, vice president of the power company, conceded that the time line for getting the overheated plant cooled down is uncertain.
"Regrettably, we don't have a concrete schedule at the moment to enable us to say in how many months or years [the crisis will be over]," Muto said.
Meanwhile, Japan's National Police Agency said Sunday that the death toll from the quake and tsunami had jumped to 10,668, with 16,574 people still missing.