Japan Tuesday raised the severity of its nuclear disaster to the highest level, putting it on a par with the world's worst disaster nuclear accident at Chernobyl, Reuters reported. The rating of the accident at the Fukushima Daiichi nuclear plant was raised from 5 to 7, the worst on the internationally recognized scale.

Japan said this reflects the initial severity of the crisis and not the current situation. An official with Japan's Nuclear Safety Commission said that the emission of radioactive substances from Fukushima plant is about 10 percent of the amount detected at Chernobyl.

On Tuesday, a magnitude 6.3 aftershock struck off the coast of Chiba, 77 km northwest of Tokyo. Shortly, a fire broke out at the Fukushima nuclear plant. Several hours later, Tokyo Electric Power Co (TEPCO) said the fire was put out.

TEPCO said the fire has had no impact on radiation levels around the plant or on the plant's cooling systems. On Monday evening, an aftershock measuring 6.6 hit Fukushima prefecture, killing one person, forcing workers to evacuate the nuclear plant and knocking out power to 220,000 households.