Survivors bowed deeply 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 2:46 pm (0546 GMT), the moment a 9.0-magnitude undersea quake hit.
It's 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. Emperor Akihito paid tribute to victims killed in the tragedy, and those struggling in its aftermath.
"Many victims still lead difficult lives in devastated areas and places that were evacuated," he said from a national theatre hall in downtown Tokyo.
"It is important for all people to join together and show their support in the long-term... I pray for a return of peaceful times to devastated areas."
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.