Update: Japan ordered inspections of ageing highway tunnels on Monday after a fiery collapse that killed nine people, as suspicion over the cause of the accident centred on decaying ceiling supports.
The government pledged a thorough review and said "significant investment" would likely be required in the motorway network, parts of which including the accident site were built during the economic boom of the 1960s and 1970s.
"As a major factor, we suspect ageing," an official from highway operator NEXCO said, referring to the tragedy at the Sasago tunnel, which passes through hills near Mount Fuji, 80 kilometres (50 miles) west of Tokyo.
Engineers on Monday began inspections at three other tunnels in the region with the same design, as well as at Sasago.
And the Ministry of Land, Infrastructure and Transport ordered emergency inspections of all 49 highway tunnels nationwide that have the same design.
NEXCO said safety inspections consist largely of visual surveys, with workers looking for cracks and other abnormalities, or listening to the acoustics of the concrete and metal parts by hitting them with hammers.
Officials admitted that during the five-yearly check of the ceiling in September there had been no acoustic survey of the metal parts on which the panels weighing up to 1.5 tonnes rest.
Emergency workers were still at the nearly five-kilometre (three-mile) tunnel Tuesday, but 24 hours after the cave-in, efforts shifted from rescue to recovery.
Three vehicles were buried on Sunday when concrete ceiling panels crashed down inside the tunnel. Witnesses spoke of terrifying scenes as at least one vehicle burst into flames.
Emergency workers had collected five charred bodies -- three men and two women -- from a vehicle by early Monday. One report said the victims were all in their 20s.
They also recovered the body of a truck driver, identified as 50-year-old Tatsuya Nakagawa who reportedly telephoned a colleague immediately after the incident to ask for help.
Three other deaths have been confirmed, an elderly man and two elderly women, who were all in the same passenger vehicle, officials said.
"I offer my deepest condolences" to those affected, NEXCO Central president Takekazu Kaneko said. "First and foremost, the rescue operation is our priority. We are also inspecting our tunnels that use the same design."
Japan's extensive highway network criss-crosses the mountainous country, with more than 1,500 tunnels. Around a quarter of these are more than 30 years old, according to the Transport Ministry.
The country is also prone to earthquakes and despite a tightening of safety regulations over the last 20 years, older structures could be vulnerable to the regular movements, experts have warned.
Chief Cabinet Secretary Osamu Fujimura said the government had ordered immediate action to shore up the transport system.
"The prime minister ordered the transport ministry to do its utmost in the rescue operation, to find out the cause at an early stage, to take thoroughly preventive measures against similar accidents," he said.
"We will have to make significant investment in public transportation systems and will need to ensure its durability. We need to review infrastructure as it ages."
Japan had an infrastructure boom in the 1960s and 1970s as the economy went through a period of spectacular growth.
But experts warn that as they age, many of tunnels and bridges will need to be replaced -- not an easy task for a government that already owes over twice what the economy is worth in a year.
Japanese rescuers found five charred bodies in a highway tunnel that collapsed on Sunday, crushing cars and triggering a blaze, and sparking fears of another cave-in.
At least seven people were missing inside the nearly five-kilometre (three mile)-long tunnel. Witnesses spoke of terrifying scenes as at least one vehicle burst into flames, sending out clouds of blinding, acrid smoke.
For several hours rescuers were forced to suspend their efforts to reach those believed trapped under 1.5-tonne concrete ceiling panels that crashed from the roof as engineers warned more debris could fall.
At least one video claiming to have CCTV images from inside the tunnel was uploaded to YouTube.
Emergency crews who rushed to the Sasago tunnel on the Chuo Expressway, 80 kilometres (50 miles) west of the capital, were hampered by thick smoke billowing from the entrance.
Dozens of people abandoned their vehicles on the Tokyo-bound section of carriageway, and ran for one of the emergency exits or for the mouth, where they huddled in bitter winter weather.
Emergency crews equipped with breathing apparatus battled around a third of the way into the tunnel, where they found 110 metres (yards) of concrete panels had come crashing down, crushing at least two vehicles.
Hours after the collapse, engineers warned the structure could be unstable, forcing rescuers to halt their work as a team of experts assessed the danger.
It was during this inspection that accompanying police officers confirmed the first deaths.
"What we found resembled bodies inside a vehicle, they were blackened. We have visually confirmed them but have yet to take them out for closer examination," an official told AFP.
The Fire and Disaster Management Agency later confirmed there were five bodies, adding another vehicle had also been burned.
Footage from security cameras in the late afternoon showed large concrete panels in a V shape, apparently having collapsed from the middle, with teams of men in protective gear scrambling over them.
A fire department official said workers were still trying to reach a van in which at least one person was believed trapped.
Chikaosa Tanimoto, professor emeritus of tunnel engineering at Osaka University told NHK the concrete panels are suspended from pillars.
"It is conceivable that the parts connecting the ceiling panels and pillars, or pillars themselves, have deteriorated, affected by vibrations from earthquakes and passing vehicles," he said.
An official from highways operator NEXCO said degradation was a possibility, adding the risk of further collapse remained.
Another official said the ceiling had undergone its regular five-yearly inspection in September this year.
One 28-year-old woman who emerged from the smoke-darkened tunnel by herself told rescuers she had been in a rented vehicle with five other people, fire department official Kazuya Tezuka told AFP by telephone.
"I have no idea about what happened to the five others. I don't know how many vehicles were ahead and behind ours," she was quoted as saying.
An AFP reporter said two large orange tents had been erected at the tunnel mouth and a helicopter remained nearby, ready to ferry the injured to hospital.
The tunnel, which passes through hills not far from Mount Fuji, is one of the longest in Japan. It sits on a major road connecting Tokyo with the centre and west of the country.
An NHK reporter was passing through the tunnel on his way to Tokyo when it started to disintegrate.
"I managed to drive through the tunnel but vehicles nearby appeared to have been trapped," he said. "Black smoke was coming and there seemed to be a fire inside the tunnel."
A man in his 30s, who was just 50 metres (yards) ahead of the caved-in spot, recounted details of the terrifying experience.
"A concrete part of the ceiling fell off all of a sudden when I was driving inside. I saw fire coming from a crushed car. I was so frightened I got out of my car right away and walked one hour to get outside," he told NHK.
Japan has an extensive and well-maintained network of highways with thousands of tunnels, usually several hundred metres long. Millions of cars use the network every day.