Survivors bowed deeply and joined hands at remembrance ceremonies in towns and cities around the disaster zone and in Tokyo, where Emperor Akihito and Empress Michiko led tributes to those who died in Japan's worst peace-time disaster.
A national moment of silence followed the cry of tsunami alarm sirens which were set off at 14:46, the moment a 9.0-magnitude undersea quake hit.
Its raw force unleashed a towering wall of water that travelled at the speed of a jet plane to the coast. Within minutes, communities were turned to matchwood, and whole families drowned.
Giant waves also crashed into the Fukushima nuclear plant, sparking reactor meltdowns and explosions, and setting off the worst atomic crisis in a generation.
The crippled plant remains volatile and the complicated decommissioning process is expected to last for decades, as fears persist over the health effects of leaked radiation. Tens of thousands were evacuated from the stricken area.
As night fell, an event in a Fukushima park saw about 2 000 lit candles arranged to read "Fukushima 3/11".
"We must sincerely regret the accident and tackle the reconstruction by keeping the hardships faced by Fukushima people in mind", Naomi Hirose, head of embattled plant operator Tokyo Electric Power, told employees at the wrecked site.
In Tokyo, Emperor Akihito paid tribute to victims killed in the tragedy, and those struggling in its aftermath.
"Many still lead difficult lives in devastated areas and places that were evacuated", he said.
"I pray for a return of peaceful times."
Although no one died as a direct result of Fukushima, about 1 650 area residents passed away from complications related to stress and other problems following the accident.
A total of 15 884 people are confirmed to have died in the tsunami with another 2 633 still listed as missing. Human remains are sometimes still found years later.
In the shattered town of Namie, just 8km from the stricken plant, about 200 former residents, police and fire-fighters searched for remains. They raked a beach where broken timber and cars pulled by the waves once lay half buried.
Nuclear fears still raw
"Our parents are still missing", said 25-year-old former resident Miho Suzuki, joined by her sister.
"I don't think we'll ever find them, but we came here to take part because we felt like doing something to help."
For another former Namie resident, Morihisa Kadoya, returning to a town that remains uninhabitable due to health concerns seems like a distant dream.
"It's impossible to come back, the decommissioning at the plant is going to take years", he said.
Despite the government pledging billions of dollars in reconstruction aid, progress in disaster-hit regions has been slow, some communities remain ghost towns, and thousands of disaster refugees struggle to cope.
Among almost 270 000 evacuees from the tsunami and Fukushima, about 100 000 are in temporary housing while others found shelter in new cities or with relatives.
Japan has so far built only 3.5% of the new homes promised to disaster refugees in heavily affected Iwate and Miyagi prefectures.
"I'm determined to accelerate the recovery and not let this disaster fade from memory", Prime Minister Shinzo Abe told parliament on Monday.
"Japan's revival won't come without the restoration of devastated areas."
On Sunday, tens of thousands came to an anti-nuclear rally in Tokyo, voicing anger at Abe's plan to switch on shuttered nuclear reactors, which had supplied more than a quarter of the resource-poor nation's power.
"Prime Minister Abe and the nuclear industry are hoping the Japanese people and the world will forget the victims and the terrible lessons of Fukushima, hoping that they will allow the restart of old, risky reactors", said Junichi Sato, executive director of Greenpeace Japan.
All of Japan's reactors were switched off after the accident, forcing the country to turn to pricey fossil-fuel alternatives to plug the energy gap.
Despite Tokyo's push to boost renewable energy, power sourced from wind farms and solar energy remains a fraction of Japan's needs. Concerns have also been raised about meeting greenhouse-gas reduction targets without atomic power.