Three men and two women in their 20s, who were travelling in the same vehicle, found dead inside the Sasago tunnel
Rescue works continue at Sasago Tunnel where concrete ceiling panels collapsed more than 110 metres and at least 9 people have been confirmed dead Photograph: The Asahi Shimbun/The Asahi Shimbun via Getty Images
Justin McCurry in Tokyo
Nine people have been found dead inside a motorway tunnel near Tokyo that collapsed and caught fire on Sunday morning, police said, as officials attempted to establish the cause of the accident.
The victims include three men and two women, all in their 20s, who were travelling in the same vehicle, Japanese media said. A woman who had been travelling with the group when the accident occurred managed to escape and was being treated for minor injuries.
Police said the bodies of a man and two women had been found in a second vehicle, while the ninth victim was confirmed as Tatsuya Nakagawa, a 50-year-old lorry driver who had called his company asking for help after the tunnel's ceiling collapsed.
Reports said as many as 150 concrete slabs, each weighing 1.2 tonnes, had crashed to the ground along a 110-metre-long stretch of the Tokyo-bound lane inside the tunnel, which connects Tokyo with central Japan.
Firefighters discovered five bodies inside a white van after battling through thick smoke on Sunday afternoon. The rescue operation was temporarily halted amid fears of another collapse.
Police said they did not know what had caused the section of the 2.5 mile tunnel, located along a busy stretch of the Chuo expressway about 50 miles west of Tokyo, to cave in.
Motorway officials believe that one of the metal rods used to secure the concrete panels to the tunnel's inner walls may have become loose, triggering a chain reaction that rained concrete onto the vehicles below.
Another theory is that the structure may have been weakened by a 4.9 earthquake that shook the Tokyo area on 24 November, or by a landslide inside the mountain through which the tunnel passes. The motorway's operator said a routine safety check conducted as recently as October had not revealed any structural faults.
Closed circuit TV footage showed rescue workers attempting to remove large chunks of concrete in a frantic effort to reach vehicles trapped beneath. More than a dozen fire engines were lined up outside both entrances to the tunnel, while fleets of ambulances waited to treat the injured.
People who were able to drive or walk out of the tunnel said panicked motorists had started driving the wrong way down the motorway after the collapse began; others said they heard people trapped beneath the concrete calling out for help.
"While I was driving through the tunnel, concrete pieces suddenly started falling from the ceiling," one man told public broadcaster NHK. "I saw a crushed car catch fire. I was scared, so I left my car and walked for about an hour to get out of the tunnel."
Earlier, firefighters had struggled to reach the scene of the accident - about a mile inside the tunnel - because falling concrete had ignited petrol leaking from trapped cars, sparking a blaze that sent thick black smoke billowing from the tunnel entrance.
Another survivor told TV Asahi he had witnessed the cave-in before calling police, who told him to flee. "A few seconds later and my car would have been right in the middle of it," he said.
Yoshio Goto, an NHK reporter who was driving through the tunnel when the roof began to cave in, said he had put his foot on the accelerator as soon as he felt pieces of concrete falling on to the roof of his car. "I was a bit too late and pieces of the roof fell on my car," Goto said. "I kept pressing the pedal and managed to get out. Then, when I looked around, I saw that half of the top of my car had been crushed."
It is not clear if emergency workers expect to find more bodies beneath the rubble. Officials had initially said seven people were feared missing inside the tunnel, which opened to traffic in
The accident, on one of Japan's busiest motorways, will inevitably raise questions about the safety of the country's large network of tunnels - motorists' quickest route through its mountainous topography.
Sunday's accident was the worst of its kind since 1996, when a tunnel in northern Japan collapsed and falling rocks crushed cars and a bus, killing 20 people.