A massive 9.0 magnitude earthquake and tsunami on March 11 knocked out the cooling systems of the Fukushima plant's six reactors triggering explosions and fires, releasing radiation and sparking global fears of a widening disaster.

TEPCO president Masataka Shimizu, 66, fell sick on March 16 and took a week off from the joint task force that had been set up by the government and the company, the Mainichi Shimbun daily said, citing company officials.

"He was not at the task force but (was) still collecting information at the headquarters (in Tokyo), giving instructions," a TEPCO spokesman was quoted saying by the Mainichi daily.

But another TEPCO employee, described as a senior official, said Shimizu had been so sick that he had stayed "mostly in bed" in a separate room in the building where the task force was meeting, the newspaper said.

He had now recovered and returned to work at the liaison office, Kyodo News said.

Shimizu has not appeared in public since attending a press conference on March 13, leading to local media criticism that he had been irresponsible.

A TEPCO spokesman declined to elaborate on his health condition, but said he did not fall over or require an intravenous drip, Kyodo said.