The footage to be released may shed light on how Tepco dealt with the No. 4 unit's spent fuel pool, the source of most concern at the U.S. nuclear regulator because it was the sole unit to hold all fuel rods without a solid containment.

It may also answer questions about the deliberate release of radioactive water into the sea by Tepco in early April -- more than two weeks after the earthquake and tsunami that triggered the crisis. Neighboring countries, including South Korea and China, denounced the release.

"We consider the first month of the disaster as a period of emergency," Tepco said in a statement late on Thursday about the extra footage. It was not clear when it would release the film covering events between March 16 and April 11.

Tepco had released 150 hours of footage covering the first five days after the March 11 quake to media only, prompting criticism that the company was not coming clean on the early days when the situation at the plant almost spun out of control.

Tepco had previously acknowledged in 2007 that it covered up safety lapses for years.

(Reporting by Risa Maeda; Editing by Ron Popeski)

• A Permanent Economic Emergency