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For 70-year-old Toshiko Murakami, memories of the terrifying earthquake and tsunami that destroyed much of her seaside town and swept away her sister brought fresh tears Sunday, exactly a year after the disaster.

"My sister is still missing so I can't find peace within myself," she said before attending a ceremony in a tent in Rikuzentaka marking the anniversary of the March 11, 2011, disaster that killed just over 19,000 people and unleashed the world's worst nuclear crisis in a quarter century.

Across Japan, people paused at 2:46 p.m. — the moment the magnitude-9.0 quake struck a year ago — for moments of silence, prayer and reflection about the enormous losses suffered and monumental tasks ahead.

Japan must rebuild dozens of ravaged coastal communities, shut down the crippled Fukushima Dai-ichi nuclear power plant and decontaminate radiated land so it is inhabitable again.

These are enormous burdens on a country already straining under the weight of an aging, shrinking population, bulging national debt and an economy that's been stagnant for two decades.

Prime Minister Yoshihiko Noda reminded the Japanese people that they have overcome many disasters and difficulties in the past and pledged to rebuild the nation so it will be "reborn as an even better place."

"Our predecessors who bought prosperity to Japan have repeatedly risen up from crises, every time becoming stronger," Noda said at a ceremony at the National Theater attended by the emperor and empress.

Later, he told a news conference he hoped to see the disaster-hit areas fully rebuilt when "babies born on the day of the disasters turn 10 years old."

The earthquake was the strongest recorded in Japan's history, and set off a tsunami that swelled to more than 65 feet in some spots along the northeastern coast, destroying tens of thousands of homes and causing widespread destruction.

All told, some 325,000 people are still in temporary housing. While much of the debris along the tsunami-ravaged coast has been gathered into massive piles, only 6 percent has been disposed of through incineration.

Very little rebuilding has begun. Many towns are still finalizing reconstruction plans, some of which involve moving residential areas to higher, safer ground — ambitious, costly projects. Bureaucratic delays in coordination between the central government and local officials have also slowed rebuilding efforts.

In Rikuzentakata, which lost 1,691 residents out of its pre-quake population of 24,246, a siren sounded at 2:46 p.m. and a Buddhist priest in a purple robe rang a huge bell at a temple overlooking a barren area where houses once stood.

At the same moment in the seaside town of Onagawa, people facing the ocean pressed their hands together in silent prayer.

Memorial services continued into the night. In Ishinomaki, survivors lit some 2,000 candles to mourn for the victims.

The memories of last March 11 are still raw for Naomi Fujino, a 42-year-old Rikuzentakata resident who lost her father in the tsunami. She escaped with her mother to a nearby hill, where they watched the enormous wave wash away their home. They waited all night, but her father never came as he had promised. Two months later, his body was found.

"I wanted to save people, but I couldn't. I couldn't even help my father. I cannot keep crying," Fujino said. "What can I do but keep on going?"

In Tokyo, anti-nuclear demonstrators waving banners, beating drums and shouting slogans marched to the headquarters of Tokyo Electric Power Co., the operator of the Fukushima nuclear plant.

As dusk fell, protesters holding candlelit lanterns linked arms to form a human chain nearly all the way around the parliament building.

Public opposition to nuclear power has grown in the wake of the Fukushima disaster, the worst since Chernobyl in 1986. The tsunami knocked out the plant's cooling systems, causing meltdowns at three reactors and spewing radiation into the air. Some 100,000 residents who were evacuated remain in temporary housing or with relatives.

Only two of Japan's 54 reactors are now running while those shut down for regular inspections undergo special tests to check their ability to withstand similar disasters. They could all go offline by the end of April if none is restarted.

The Japanese government has pledged to reduce reliance on nuclear power, which supplied about 30 percent of the nation's energy before the disaster, but says it needs to restart some nuclear plants during the transition period.

Emperor Akihito, 78, who recently underwent heart bypass surgery, voiced concern in a speech at the national memorial ceremony about the difficulty of decontaminating land around the plant. Workers are using everything from shovels and high-powered water guns to chemicals that absorb radiation, but it is huge, costly project fraught with uncertainty.

The Environment Ministry expects it will generate at least 130 million cubic yards (100 million cubic meters) of soil, enough to fill 80 domed baseball stadiums.

"We shall not let our memory of the disasters fade, pay attention to disaster prevention and continue our effort to make this land an even safer place to live," Akihito said.

In December, the government declared that the crippled Fukushima plant was basically stable and that radiation has subsided significantly. But the plant's chief acknowledged recently that it remains in a fragile state, and makeshift equipment — some mended with tape — is keeping crucial systems running.

Enormous risks and challenges lie ahead at the plant, including locating and removing melted nuclear fuel from the inside of the reactors and disposing spent fuel rods. Completely decommissioning the plant could take 40 years.

Noda has acknowledged failures in the government's response to the disaster, including being too slow in relaying key information and believing too much in "a myth of safety" about nuclear power.

In a statement from Vienna marking the anniversary, the International Atomic Energy Agency called the Fukushima accident "a jolt to the nuclear industry, regulators and governments."

Although it was triggered by a natural disaster, the accident highlighted "existing weaknesses" in regulatory oversight, accident management and defense against natural hazards, the IAEA said.

For Tamiko Oshimizu, the day brought a sense of closure.

Shown on TV wearing protective coveralls and a surgical mask to protect against radiation as she joined a small group of evacuees entering the 12-mile no-go zone around the Fukushima plant, she placed a bouquet at the site of her aunt and uncle's former house in Namie.

"You must have been so scared," Oshimizu said, referring to her relatives, who perished in the tsunami. "Until today I was not able to accept the reality. But today I'm going to face it and move on."