VIENNA - The International Atomic Energy Agency (IAEA) said on Tuesday that although Japan has raised the severity level of the accident at the Fukushima No 1 plant, the crisis is quite different from the 1986 Chernobyl accident.

"The mechanics of the accidents are totally different," deputy head of IAEA Denis Flory told the press.

Related readings:  Japan raises nuclear crisis to same level as Chernobyl  Radiation leakage in Japan may exceed Chernobyl  Japan mulls spinning off part of nuclear operator  Japan sets to extend nuclear evacuation zone

While Chernobyl accident involves explosion at the reactor core, and the resulting fire and vapors drove a large quantity of radioactive material into the air and surrounding areas, explosions at Fukushima No 1 plant happened outside the pressure vessel which contains the reactor core, Flory said.

He noted that the Japanese nuclear safety authority has estimated that the amount of radioactive material released from the Fukushima No 1 plant to the atmosphere is approximately 10 percent of the Chernobyl accident.

Flory also confirmed that Japanese authorities formally notified the IAEA that the accident is now rated as a level 7, the most serious on an international scale, from the previous 5.

Listed as "Major Accident" on the International Nuclear and Radiological Event Scale, Level 7 is used to describe an event comprising "A major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures," according to an IAEA statement.

On a positive note, Flory said although situation remains very serious, "there are early signs of recovery in some functions such as electrical power and instrumentation. "