KORIYAMA, Japan — Japanese officials warned of a possible second explosion Sunday at a nuclear plant crippled by the earthquake and tsunami as they raced to stave off multiple reactor meltdowns, but they provided few details about whether they were making progress. More than 180,000 people have evacuated the area, and up to 160 may have been exposed to radiation.
Four nuclear plants in northeastern Japan have reported damage, but the danger appeared to be greatest at the Fukushima Dai-ichi nuclear complex, where one explosion occurred Saturday and a second was feared. Operators have lost the ability to cool three reactors at Dai-ichi and three more at another nearby complex using usual procedures, after the quake knocked out power and the tsunami swamped backup generators.
Chief Cabinet Secretary Yukio Edano said Sunday that a hydrogen explosion could occur at Dai-ichi's Unit 3, the latest reactor to face a possible meltdown. That would follow a hydrogen blast Saturday in the plant's Unit 1.
"At the risk of raising further public concern, we cannot rule out the possibility of an explosion," Edano said. "If there is an explosion, however, there would be no significant impact on human health."
Operators have been dumping seawater into units 1 and 3 in a last-ditch measure to cool the reactors. They were getting water into the other four reactors with cooling problems without resorting to corrosive sea water, which likely makes the reactors unusable.
Edano said residents within about 12 miles (20 kilometers) of the Dai-ichi plant were ordered to evacuate as a precaution, and the radioactivity released into the environment so far was so small it didn't pose any health threats.
Such statements, though, did little to ease public worries.
"First I was worried about the quake," said Kenji Koshiba, a construction worker who lives near the plant. "Now I'm worried about radiation." He spoke at an emergency center in Koriyama, about 40 miles (60 kilometers) from the most troubled reactors and 125 miles (190 kilometers) north of Tokyo.
At the makeshift center set up in a gym, a steady flow of people — mostly the elderly, schoolchildren and families with babies — were met by officials wearing helmets, surgical masks and goggles.
About 1,500 people had been scanned for radiation exposure, officials said.