Japan is set to mark the first anniversary of the devastating earthquake and tsunami which struck the north-eastern coast, killing thousands.
The magnitude 9 quake, the most powerful since records began, also triggered a serious nuclear accident at the Fukushima Daiichi nuclear plant.
Thousands of people were evacuated as radiation leaked from the plant.
Memorial services have been planned and a minute of silence will be observed at the exact moment the quake hit.
The main memorial ceremony will be held at Tokyo's National Theatre and will be attended by Japan's Emperor Akihito and Prime Minister Yoshihiko Noda.
The 78-year-old emperor had heart surgery three weeks ago and reports say he will attend 20 minutes of the hour-long ceremony with Empress Michiko.
Warning sirens will sound across the north-east of the country on Sunday at the precise time the quake struck. Bells and prayers will also reverberate across the country as the minute of silence is observed.
Japan's Kyodo news agency also reported that some trains in and around Tokyo will stop to mark the moment.
The earthquake hit at 14:46 local time about 400km (250 miles) north-east of Tokyo on 11 March 2011.
Shortly after the quake, an immense surge of water enveloped the north-eastern coast as a tsunami swept cars, ships, and buildings away, crushing coastal communities.
The twin natural disasters claimed more than 15,700 lives, and more than 4,500 people remain unaccounted for.
In the Fukushima prefecture, where the Fukushima Daiichi nuclear plant is located, the impact of the disaster was particularly acute.
Radiation leaked from the plant after a series of fires and explosions damaged four of the plant's six reactor buildings, with serious failures in the plant's cooling system being at the heart of the problem.
A 20 km (12.5 mile) exclusion zone around the plant was put in place making tens of thousands of people homeless. Radiation means the area around remains uninhabitable.
The plants is in cold shutdown now and Prime Minister Noda has promised that over the decades to come it will be decommissioned and he has also pledged to rebuild the devastated towns along the coast.
But correspondents say that Japan is still dealing with the economic and political fallout of the disaster. Japan's prime minister at the time of the disaster, Naoto Kan, resigned months later.
He had been criticised for failing to show leadership during the nuclear crisis after the quake. The nuclear crisis also revealed serious flaws in the nuclear industry's regulatory systems and safety standards.
Although much of the debris has been cleared, survivors from the devastated north-east have complained about slow recovery efforts.
One day before national commemorations, the families and loved ones of victims began to pay their respects at the graves of those they have lost.
In Iwaki City in Fukushima, thousands of candles were lit, ceremonial bells were rung and monks chanted.
Anti-nuclear protests are also scheduled to be held in Tokyo, Fukushima and other parts of the country to coincide with the anniversary.