Ceremonies to mourn the dead and rallies against nuclear power were scheduled to take place across Japan on Sunday as the nation marks six months since the March 11 earthquake and tsunami.
Silent prayers are to be offered at 2:46 pm, the moment the quake struck six months ago triggering a tsunami that devastated swathes of Japan's northeastern coastline and sparked a disaster at the Fukushima Daiichi nuclear plant.
But remembrance plans were overshadowed by early embarrassment for Prime Minister Yoshihiko Noda's new government after trade minister Yoshio Hachiro resigned Saturday over comments deemed insensitive to Fukushima evacuees.
Noda has pledged his government will boost post-disaster recovery efforts but the resignation of one of his cabinet ministers will do little to stem an erosion of faith in Japan's leaders following the March disasters.
Noda on Saturday travelled to ravaged Miyagi and Iwate prefectures for the first time since taking office nine days ago, when he replaced Naoto Kan who resigned amid criticism over his handling of the crisis.
The government has been criticised for its response to the disaster, amid suspicions it underplayed the full scale of the nuclear crisis, and as political infighting overshadowed recovery efforts.
The raging wall of water unleashed by the record 9.0 magnitude quake left an indelible scar along Japan's northeastern coast, leaving 20,000 dead or missing and triggering the worst nuclear crisis since Chernobyl in 1986.
Rebuilding the muddy wastelands of the northeastern "Tohoku" region is expected to cost hundreds of billions of dollars and take up to a decade. Areas close to the Fukushima Daiichi nuclear plant may be uninhabitable for longer.
Radiation fears are a daily fact of life after cases of contaminated water, beef, vegetables, tea and seafood due to the Fukushima accident. The government has been at pains to stress the lack of an "immediate" health risk.
The towering wall of water battered cooling systems at the Fukushima plant, 220 kilometres (138 miles) northeast of Tokyo, leading to reactor meltdowns and the spewing of radiation, forcing tens of thousands to evacuate.
A day ahead of the anniversary, survivors in Soma in Fukushima prefecture held a memorial ceremony for the 459 people dead or missing from the city.
"I promise to address the reconstruction with all my strength and all my heart," said Fukushima governor Yuhei Sato as he stood in front of a stage full of white chrysanthemums.
Hundreds of paper lanterns were released into the sky there at dusk on Saturday, symbolising the souls of those lost in the disaster.