Every wing of the Self Defence Forces was thrown into frantic service, with hundreds of ships, aircraft and vehicles headed to the Pacific coast area where at least 1,000 people were feared dead and entire neighbourhoods had vanished.
International search and rescue teams also rushed to the devastated country, some fresh from work in quake-hit New Zealand -- including a 63-strong Japanese team that spent two weeks helping after the 6.3-magnitude Christchurch quake.
As emergency staff in Japan dug through rubble and plucked survivors off the roofs of submerged houses, Prime Minister Naoto Kan warned that day one after the catastrophe was a crucial window for survivors.
"I realised the huge extent of the tsunami damage," the centre-left premier said after taking a helicopter tour of the apocalyptic scenes in the northeast before meeting his cabinet ministers for an emergency meeting in Tokyo.
"What used to be residential areas were mostly swept away in many coastal areas and fires are still blazing there," he told them.
The United States, with almost 50,000 troops stationed in Japan, ordered a flotilla including two aircraft carriers to the region to provide aid -- just one of scores of nations that have offered help since Friday's monster quake.
US forces yesterday helped Japan rapidly react by delivering a cooling agent to a nuclear plant where malfunctions threatened a dangerous meltdown.
In the utter bleakness on the east coast of Japan's main Honshu island, where at least 3,600 houses were destroyed by the 8.9-magnitude quake, there were some rays of hope amid the carnage of smashed towns and shattered lives.
Army helicopters airlifted people off the roof of an elementary school in Watari, Miyagi prefecture, and naval and coastguard choppers did the same to rescue 81 people from a ship that had been hurled out to sea by the tsunami.
But for every piece of good news, there were more reminders of nature's cruelty against this seismically unstable nation -- including the latest of a series of strong aftershocks in the morning, measuring a hefty 6.8.
In large coastal areas, entire neighbourhoods were destroyed, with unknown numbers of victims buried in the rubble of their homes or lost to the sea, where cars, shipping containers, debris and entire houses were afloat.
The coastal city of Rikuzentakata in Iwate prefecture was almost completely destroyed and submerged, said the Fire and Disaster Management Agency.