Japan today said, radiation from quake-stricken Fukushima Daiichi nuclear plant has reached harmful levels. The warning comes after the plant was rocked by a third blast, which has reportedly damaged one of the reactors' containment systems for the first time. Reactor 2 became the third to explode in four days at the Fukushima Daiichi plant. Authorities have extended the danger zone, warning residents within 30kilometers to evacuate or stay indoors. The government later said that radiation levels at the plant's main gate had fallen sharply. According to BBC, a fire also briefly broke out at reactor 4, and is believed to have caused radioactive leaks. Reactor 4 had been shut down before the quake for maintenance, but its spent nuclear fuel rods are still stored on the site. Chief Cabinet Secretary Yukio Edano said they are closely watching the remaining two reactors at the plant, five and six, as they had begun overheating slightly.The crisis was prompted by last Friday's 9.0-magnitude quake and tsunami in north-eastern Japan.Meanwhile, A strong and shallow earthquake jolted Shizuoka Prefecture and its vicinity, including Tokyo, this evening. The U.S. Geological Survey said, the quake measuring 5.8 on the Richter scale jolted off the east coast of Honshu at a depth of one km. No tsunami warning has been issued.