The amount of radiation released from the crippled Fukushima Daiichi nuclear plant in the immediate aftermath of Japan's earthquake and tsunami were twice the level that the country's Nuclear and Industrial Safety originally admitted, Japan's Emergency Response Center said.

NISA, which previously held that the amount of radiation initially leaked was as low as 370,000 terabecquerels, has revised its estimate to 770,000 terabecquerels. A terabecquerel is equal to one trillion becquerels. A becquerel is a unit of radioactivity equal to one nuclear decay per second.

The new estimate does not alter the fact that the amount of radiation leaked at Fukushima is but a fraction compared to Russia's Chernobyl disaster, but it does put the amount closer in line to some outside estimates.

The new figure refers to the amount of radiation released from March 11, the day of the accident, to March 16.

It is the latest of a several revisions the Japanese agencies have made regarding the extent of the damage at the nuclear plant.

The Fukushima power plant experienced full meltdowns at three reactors in the wake of the earthquake and tsunami, the Emergency Response Center said.

The nuclear group's new evaluation, released Monday, goes further than previous statements in describing the extent of the damage.

The announcement will not change plans for how to stabilize the Fukushima Daiichi plant, the agency said.

Reactors 1, 2 and 3 experienced a full meltdown, it said.

The earthquake and tsunami knocked out cooling systems at Fukushima Daiichi, causing the three operating reactors to overheat. That compounded a natural disaster by spewing radioactive material into the atmosphere.

Tokyo Electric has avoided using the term "meltdown," and says it is keeping the remnants of the core cool. But U.S. experts interviewed by CNN after the company's announcement in May said that while the company may be containing the situation, the damage had already been done. CNN's Kyung Lah contributed to this report.