Video footage released Monday shows the head of the Fukushima nuclear power plant shouting "We have a big problem, a big problem!" as a reactor exploded after last year's quake-tsunami disaster.

The footage was among 150 hours of video conferencing recorded during the first days of the nuclear disaster reluctantly released by Tokyo Electric Power Company (TEPCO) which operated the plant.

The images showed tense exchanges as company officials struggled with the unfolding disaster after the deadly tsunami on March 11, 2011 damaged emergency power for cooling systems at the Fukushima Daiichi nuclear plant, which went through meltdowns and explosions.

Among the most tense footage recorded was on March 14 when the building covering the number three reactor exploded due to a build-up of hydrogen.

Plant chief Masao Yoshida is heard urgently reporting the blast to his bosses at TEPCO's Tokyo headquarters, more than 200 kilometres (125 miles) away.

"The head office, the head office! We have a big problem, a big problem!" Yoshida suddenly shouts during a teleconference.

"The number three reactor, it's perhaps water steam, there was an explosion! 11:01 am!" he says, his voice cracking.

A calm male voice from the TEPCO headquarters responds: "11:01 am. Acknowledged. An emergency communication."

"Those out in the field have to pull back, pull back!" says another male voice from the headquarters.

TEPCO reluctantly released about 150 hours of video covering March 11 through 15, 2011 more than a year after the accident under pressure from Industry Minister Yukio Edano.

Then-prime minister Naoto Kan was also seen rushing to TEPCO headquarters to vent his anger over the utility's clumsy handling of the crisis.

TEPCO had refused to release the footage, saying it was for internal use only, despite demands from journalists and outside experts who said it should be released for the public to analyse exactly how the accident was handled.

Of the video released, about 50 hours had sound while the rest did not.

The names and faces of TEPCO workers were blurred to protect their privacy and safety as the firm had come under serious public criticism, TEPCO said.

TEPCO is letting accredited journalists to view the footage at its headquarters until September 7 but has banned them from recording it, except for taking notes.

The utility handed out 90 minutes of selected video clips from the total footage.