The command centre at Japan's Fukushima Daiichi nuclear plant shook violently when hydrogen exploded at one reactor critically damaged by a massive tsunami, and the plant chief shouted, "This is serious! This is serious!" newly released videos taken during the March 2011 crisis reveal.

Tokyo Electric Power Co. initially refused to release the footage, but the company is now under state control and was ordered to do so. The videos, seen Monday, are mainly of teleconferences between company headquarters in Tokyo and staff at the nuclear plant after the tsunami damaged several of its reactors.

In the videos, then-plant chief Masao Yoshida can be heard complaining about phone calls to the prime minister's office not getting through and expressing frustration over interference from government nuclear safety officials whose technical advice didn't fit conditions at the stricken plant.

Workers watch explosion on TV

In footage taken around 11 a.m. on March 15, Yoshida screams to utility officials: "Headquarters! This is serious, this is serious! The No. 3 unit. I think this is a hydrogen explosion. We just had an explosion.

"I can't see anything from here because of heavy smoke."

Workers wearing protective suits remove unused nuclear fuel assemblies stored in the spent fuel pool of the No. 4 reactor at the Fukushima plant on July 18, 2012, four months after a massive tsunami caused a meltdown at the site. (Handout /Tokyo Electric Power Co./Reuters)

In the background, officials can be heard shouting questions about radiation levels and other data. The massive earthquake and tsunami that hit northeast Japan knocked out the cooling systems that kept the reactors' nuclear material stable, causing a meltdown of the three reactors' cores, releasing large amounts of radiation.

As workers struggled to assess the situation, they fell behind media reports. A voice from an off-site emergency centre says he saw the explosion on television news.

The structures housing three of the reactors suffered hydrogen explosions after gas filled the unvented buildings, and the blasts spewed radiation and delayed repair work. To try to halt the explosions, the videos show officials even considered dropping a hammer from a helicopter to make a hole in the ceiling, but they scrapped the idea because it was too dangerous.

Officials murky on evacuation procedures

The footage reveals communication problems between the plant and the government as well as workers' lack of knowledge of emergency procedures and delays in informing outsiders about the risks of leaking radiation.

Just after the Unit 3 explosion, plant officials and TEPCO executives discussed extensively whether to call it a hydrogen explosion. The videos also showed they failed to notify officials outside TEPCO and residents about the March 14 meltdown at another unit, No. 2, or even provide data crucial for evacuation.

"Are we providing a release on this?" TEPCO vice-president Sakae Muto asks while discussing the meltdown of Unit 2's reactor core. A plant worker says no, while another executive, Akio Komori, instructs workers to quickly conduct radiation monitoring because they might have to evacuate at some point.

To this, another TEPCO official replies that he does not know the evacuation procedures contained in an emergency manual: "Sorry, that's not in my head."

Limits of radiation exposure pushed

After the March 12 explosion at Unit 1, dozens of workers were highly exposed to radiation, and the videos reveal TEPCO officials debated how they could allow extra exposures without getting in trouble.

"They can go home and take a bath and open their pores" to wash off contamination, one official suggests. Days later, the government raised the maximum exposure levels to more than double the usual limit for emergency operation.

The Unit 2 reactor was the most critical in the first few days. "Radiation levels are extremely high," Yoshida said. "You don't understand because you're not here, but it's really a skin-tight situation. (The workers) can go in only a short while, and they have to rotate."

The 150 hours of footage were heavily edited, with workers' faces obscured and beeps masking voices and other sound. In addition, TEPCO made a 90-minute video of selected clips available for download.

PM's visit brings stern rebuke

On March 15, the videos show a visit by then-prime minister Naoto Kan to TEPCO's Tokyo office. Bursting in, Kan is seen rebuking officials and demanding they work harder, though the segment contains no sound. For 20 minutes, operations at Fukushima Daiichi seem halted, with officials and workers, as well as TEPCO executives in Tokyo, sitting straight and quietly listening to him.

Then prime minister Naoto Kan, right, speaks to an employee of the Tokyo Electric Power Co. clad in a protective suit to guard against radiation as he visits J-Village in Fukushima Prefecture on April 2, 2011. Kan was criticized for his handling of the disaster. (File/Prime Minister's Office of Japan/Associated Press)

Shown from behind, Kan appears upset, frequently raising and lowering his arms. Government and parliamentary investigation reports have said that Kan, who thought TEPCO executives planned to fully withdraw workers and abandon the plant, demanded they "risk their lives" to get the plant under control.

Eventually, a total of 71 workers remained, trying to avoid catastrophe.

The plant's reactors were declared stable in December, and many more workers are now toiling at the site, undertaking a cleanup that could take decades. More than 160 workers have exceeded radiation exposure limits that require they no longer work at the plant, but so far, no one is known to have developed a radiation-induced illness.

Kan left office last year after being criticized for the government's failings during the disaster, which was the world's second-worst nuclear accident after Chornobyl.