Rescuers intensified the hunt for nine people still missing in a devastated village in southern Japan on Monday, with time running out after two powerful earthquakes left buildings in rubble and houses buried in mud.
At least 42 people are known to have died after the earthquakes struck the island of Kyushu, officials said, and the missing are feared buried in houses that have been engulfed by landslides.
Up to 25,000 personnel have fanned out through villages where scores of traditional-style houses have been left in ruins by Saturday's 7.0 magnitude quake, which struck a part of Japan not used to such tremors.
Prime Minister Shinzo Abe said the government was working tirelessly to find survivors, and the US military has also sent troops and aircraft to help with relief efforts.
"There are individuals still missing," he told reporters. "We will continue to give our all for search and rescue activities."
In badly hit Minami-Aso, dozens of soldiers from Japan's Self-Defence Force were working with local disaster rescuers and search dogs to find four people thought to be buried in up to 20 metres (66 feet) of earth.
"The mud here is so soft and mixed with air, so it is still moving downward as many aftershocks hit," rescuer Tsukasa Goto told AFP, adding that at least four houses have been swept away.
"The heavy machines came finally this morning as they were blocked by roads that were broken and cut off."
An official with Kumamoto prefecture said the toll of missing had fallen to nine from 10.
Rescuers are racing against time to find people before they are buried by more landslides caused by the hundreds of aftershocks that have rocked the area.
More than 110,000 people have been evacuated in Kumamoto, the central government said, many of them forced to sleep in temporary accommodation or huddled in makeshift shelters.
Thursday's initial quake, measured at 6.2 magnitude by US geologists, affected older buildings and killed nine people. But Saturday's more powerful tremor brought even newer structures crashing down.
"I could hear a rumbling sound soon after the quake," Minami-Aso resident Yoko Eto, 38, told AFP.
"It felt like only a few minutes before the water came rushing through the ground floor."
Isolated villages in mountainous areas have been completely cut off by landslides and damage to roads.
Aerial footage showed a bridge on a main trunk road had crashed onto the carriageway below, its pillars felled by the huge seismic jolt.
More than 400 aftershocks have rocked Kumamoto and other parts of central Kyushu, an area unaccustomed to the powerful quakes that regularly rattle other parts of Japan.
The US military, which has almost 50,000 servicemen and women stationed in Japan, was also taking part in rescue activities.
Tilt-rotor Osprey aircraft were among those taking part in relief efforts, the US Marines said.
Concern about the impact of the earthquakes also hit Japan's financial markets, where stocks slumped more than three percent on Monday.
The damage looked set to affect industry, with car giant Toyota announcing the gradual suspension of assembly lines nationwide, citing problems with parts suppliers in the area.
Honda said its motorcycle plant in Kumamoto will also remain shut until Friday.
Japan is one of the world's most seismically active countries, sitting on the so-called 'Ring of Fire' around the Pacific tectonic plate.
A huge undersea quake in March 2011 killed around 18,500 people when it sent a devastating tsunami barrelling into the northeast coast, sparking a nuclear disaster at Fukushima.