An explosion Tuesday morning at a Japanese nuclear plant damaged by the country's devastating earthquake and tsunami has elevated the risk of more radiation leaks to very high, as the country struggles to respond to the mounting human disaster. The Fukushima Dai-ichi facility's precarious state was underscored by the details trickling out in the wake of the blast at the Unit 2 reactor. It was the third explosion in four days at the nuclear plant, and the condition of the Unit 2 reactor is of greatest concern to authorities. "The level seems very high, and there is still a very high risk of more radiation coming out," Prime Minister Naoto Kan said in a nationally televised statement. Radiation has spread from the three reactors of the Fukushima Dai-ichi nuclear plant, Kan said, and he warned there are dangers of more leaks and told people living within 12 miles of the complex to evacuate and people within 19 miles to stay indoors to avoid radiation sickness. A fire at a fourth reactor that was extinguished by Tuesday afternoon further escalated concerns, as Chief Cabinet Secretary Yukio Edano said more radiation had been released.