TOKYO | Japan grieved Sunday over its losses in the wake of a massive earthquake and tsunami that devastated the country Friday and triggered a nuclear-power crisis officials were still trying to deal with Monday.
The 9.0 magnitude earthquake, the worst to hit Japan, and the tsunami that followed with 30-foot-high waves may have killed as many as 10,000 people and battered a 1,300-mile stretch of coastline, wiping out whole towns and villages.
A volcano on the other side of Japan from the epicenter of the quake resumed eruptions of ash and rocks, after weeks of inactivity, Japan’s weather service said Sunday. However, officials added that the fresh eruptions at the Shinmoedake volcano may be unrelated to the earthquake.
Meanwhile, nuclear officials Sunday were scrambling to prevent a second reactor from exploding at the nuclear-power plant in Fukushima province, where a reactor exploded Saturday and neared meltdown.
Japanese Chief Cabinet Secretary Yukio Edano said that a hydrogen explosion could occur at Unit 3 of the Fukushima complex, after a blast at a building housing a reactor the day before at Unit 1.
“At the risk of raising further public concern, we cannot rule out the possibility of an explosion,” he said. “If there is an explosion, however, there would be no significant impact on human health.”
As Japanese authorities tried to downplay the nuclear crisis in northeastern Japan, nuclear scientists and activists here warned of dangerous scenarios if workers fail to cool the second reactor.
Masashi Goto, an engineer who formerly designed nuclear plants for Toshiba, which built the troubled reactors in Fukushima, called the crisis facing Japan an “extraordinary situation.”
“If the cooling process stops, the radiation can’t be contained anymore,” he told a panel at the Foreign Correspondents Club of Japan on Sunday night in Tokyo. “The government is saying reassuring words to say everything is all right. But the public needs to understand that this is beyond what the reactor was designed to withstand.”
Japan’s Kyodo News agency quoted a Fukushima government official as saying that 19 evacuees were found exposed to radiation, while 160 people — including 60 elderly hospital patients and staff — may have been contaminated. Ryo Miyake, a spokesman for Japan’s nuclear agency, confirmed that 160 people may have been exposed.
Mr. Goto said that attempts to cool nuclear rods with seawater are potentially dangerous, and he warned of a chain reaction of explosions at the 40-year old plant.
“If it’s a steam explosion, it’s comparable to a volcano erupting and lava flowing into the ocean. It’s very, very serious and frightening,” he said.
Mr. Goto was cautious not to speculate on potential damage to public health, saying only that radiation could travel beyond a 12-mile zone where the government has ordered an estimated 170,000 residents to evacuate.
“I can’t predict how long it will take for this situation to settle because nobody knows exactly what the situation is inside the reactor,” he said.
Philip White, international liaison officer of the Citizens’ Nuclear Information Center, a group of about 10 activists originally formed by nuclear scientists in Japan, says the plant is in “a state of meltdown.”
“You are not safe if you are 21 kilometers [13 miles] away,” he said in an interview, when asked if a meltdown could threaten people in Tokyo, about 155 miles southwest of the reactor.
“In a worst-case scenario, radiation could come to Tokyo if the wind was blowing in the right direction,” he said.
“A nuclear disaster, which the promoters of nuclear power in Japan said wouldn’t happen, is in progress. We warned that Japan’s nuclear power plants could be subjected to much stronger earthquakes and much bigger tsunamis than they were designed to withstand.”
International officials, experts and activists differed on the potential fallout in Japan.
“This is not a serious public health issue at the moment,” said Malcolm Crick, secretary of the U.N. Scientific Committee on the Effects of Atomic Radiation.
“It won’t be anything like Chernobyl. There the reactor was operating at full power when it exploded, and it had no containment,” he said, referring to the world’s worst nuclear-power accident, in Ukraine in 1986.
“Many people thought they’d been exposed after Three Mile Island,” he said of the nuclear accident in Pennsylvania in 1979. “The radiation levels were detectable; but in terms of human health, it was nothing.”
Authorities in Japan, meanwhile, urged people near the plant to stay inside, shut windows, and wear clothing to protect their skin from potential radiation.
The earthquake and tsunami killed 1,400 people, according to official estimates. Hundreds are missing. However, police in one of the worst-hit areas feared the death toll could reach 10,000.
At least 1.4 million households remained without water Sunday, and 2 million households had no electricity. Officials plan to begin power rationing with rolling blackouts Monday in several cities, including Tokyo.
The government also doubled the number of troops pressed into rescue operations to about 100,000.
Dozens of countries have offered assistance. Two U.S. aircraft carrier groups were off Japan’s coast and ready to help. Helicopters were flying from one of the carriers, the USS Ronald Reagan, delivering food and water.
Two other U.S. rescue teams, including one from Fairfax County, Va., and rescue dogs arrived Sunday.
• This article is based in part on wire service reports.