TOKYO — Nine people were found dead early Monday after their cars were crushed by slabs of concrete that fell from the ceiling of a tunnel in eastern Japan, severing a major highway leading to Tokyo.
The police said they were investigating the cause of the collapse on Sunday at the Sasago Tunnel — a three-mile passage near the city of Otsuki and about 50 miles west of Tokyo — and for evidence of negligence by the company that operates the highway.
News reports said investigators believed that supports in the ceiling of the 35-year-old tunnel might have grown brittle, allowing hundreds of the slabs to fall onto passing vehicles. Each slab weighed 1.2 tons, officials said.
The concrete crushed three vehicles, including a van carrying six people that caught fire, filling the tunnel with thick, black smoke. Only one of the van’s occupants, identified as a 28-year-old woman who worked at a bank in suburban Tokyo, was able to escape, the police said.
Firefighters found the bodies of five other people from the van after putting out the fire and determining that the ceiling was safe enough to permit rescue efforts. They also found two other vehicles, one a truck whose driver’s body was found in the cab, the other a sedan carrying three people who were killed.
The truck belonged to a wholesale company, the police said. The 50-year-old driver had called the company right after the collapse to ask for help, but was not heard from again, news reports said.
The collapse caused a long traffic backup on one of the main highways into Tokyo. Television news reports showed smoke billowing from the tunnel entrance as motorists abandoned their cars or tried to turn in the other direction.
Drivers and passengers who got out of the tunnel told the local news media that they had escaped on foot, some leading children for half an hour before they got outside. Sasago Tunnel runs through a mountain near Mount Fuji in Yamanashi Prefecture.
Some of the survivors said that they could hear cries from the trapped cars, but that smoke and fears of another collapse prevented them from trying to help. The bank worker who escaped from the van identified the other occupants as her boyfriend and two other couples, all in their 20s.
“I could hear voices of people calling for help, but the fire was just too strong,” the woman said in an interview with public broadcaster NHK.
The highway’s operator, Central Nippon Expressway Co., said supports made of concrete and metal suddenly gave away, causing a 350-foot section of the ceiling to fall. The company said a routine inspection of the tunnel in September failed to find any signs of danger.
In a news conference at its headquarters in the central city of Nagoya, the company apologized for the accident.
The accident will close a section of the Chuo Expressway, which connects Tokyo to western Japan, for an undetermined length of time. Local news reports said officials would direct drivers to alternative routes through the mountains until the tunnel is cleared and repair work can be completed.
The accident raised questions about whether other tunnels and highway infrastructure built during the construction boom of the 1960s and ’70s are growing too old and need to be strengthened or replaced. Long tunnels — usually lined with smooth, white concrete — are common on highways in the mountainous island nation.
In 1996 a tunnel in Hokkaido in northern Japan collapsed and falling rocks crushed cars and a bus, killing 20 people. Officials said a huge shard of rock weighing about 21,000 tons smashed through the Toyohama Tunnel near Yoichi in western Hokkaido.
In that accident, police referred highway officials to prosecutors for investigation of whether the deaths resulted from professional negligence, but investigators determined that the rock fall could not have been foreseen.
Large earthquakes are common in Japan, but none was reported in the area Sunday.