The good news is that a major meltdown has apparently been averted at the Fukushima power plant in northern Japan, after the reactor was flooded with seawater. Also good news: the explosion that was seen yesterday was not inside the reactor itself.

TOKYO — Japanese officials took the extraordinary step on Saturday of flooding a nuclear reactor with seawater in a last-ditch effort to avoid a nuclear meltdown, after an explosion there escalated the emergency caused by the huge earthquake and tsunami that destroyed parts of the country’s northeastern coast on Friday.

Officials said late Saturday that leaks of radioactive material from the plant, in northern Japan, were receding and that a major meltdown was no longer imminent. But the government doubled its evacuation radius around the plant to 12 miles, and the worries about radiation and chaos from tens of thousands of people fleeing the area hampered efforts to search for survivors and forced Japan’s leadership to grapple with two major crises at once.