Japanese rescuers have found five charred bodies and a trucker was pronounced dead after being pulled from his vehicle following the collapse of a highway tunnel, which crushed cars and triggered a blaze.
At least three vehicles - including a car, a truck and a wagon - were buried when concrete panels came crashing down inside the nearly five-kilometre-long tunnel, police said, according to Jiji Press news agency.
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 the more-than one tonne concrete ceiling panels that crashed from the roof as engineers warned more debris could fall.
Emergency crews who rushed to the Sasago tunnel on the Chuo Expressway, 80 kilometres 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 workers equipped with breathing apparatus battled around a third of the way into the tunnel, where they found 110 metres of concrete panels had come crashing down, crushing several 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 confirmed there were five bodies, adding another vehicle had also been burned.
Police later said a man had been rescued from a truck buried under the concrete but that he was pronounced dead in hospital, according to Jiji Press.
Rescuers had initially said they believed at least seven people were missing in the collapse.
One man who fled the tunnel told Jiji Press he had watched in horror as concrete crashed down onto a vehicle in front of him, leaving little more than a mound of dust and debris.
Voices cried out "Help" and "Anyone please help" from the pile before a young woman emerged with her clothes torn, he was reported as saying.
She could not stop trembling, he told the agency, as he asked her how many had been inside the vehicle.
"She said: 'All of my friends and my boyfriend...Please help them,"' said the man, adding the flames were too strong.
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.
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.
Earthquakes are common in Japan, though none were reported in the area at the time of the collapse.
An official from highways operator NEXCO said material degradation was a possibility, adding the risk of further collapse remained. His colleague said the ceiling had undergone its regular five-yearly inspection in September this year.
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 near 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.
A man in his 30s, who was just 50 metres 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 web of highways with thousands of tunnels, usually several hundred metres long. Millions of cars use the network every day.