The Japanese government has ordered emergency inspections of road tunnels across the country following a deadly roof collapse west of Tokyo.
Nine people were confirmed dead after concrete panels collapsed and started a fire in the Sasago tunnel, 80km (50 miles) from the capital on Sunday.
An inquiry into the Sasago collapse has also been launched.
Officials from the highway operator suggested that metal rods securing the concrete panels may have loosened.
Japanese media report that the ministry of land, infrastructure, transport and tourism has ordered highway operators overseeing tunnels similar to Sasago to carry out emergency inspections.
A total of 49 other tunnels on roads managed by the government are being inspected, the ministry said.
Japan's highway network has more than 1,500 tunnels and officials estimate that about a quarter of these are more than 30 years old.
The BBC's Rupert Wingfield-Hayes in Tokyo says the new inspections will be more intrusive.
He says the focus of the investigation into the Sasago incident will consider why an inspection just two months ago did not spot anything wrong.
In the accident, 270 concrete slabs, each weighing 1.4 tonnes, came crashing down at about 08:00 local time on Sunday (23:00 GMT Saturday).
Japanese media say that the company that owns Sasago had relied on rudimentary visual inspections there, with no reinforcement or repairs since construction in 1977.
Officials are also quoted as saying that during the regular checks of the tunnel's ceiling, there had been no acoustic survey of the metal pieces on which the panels which collapsed rest.
Motohiro Takamisawa, from Central Nippon Expressway (Nexco), which operates Sasago, said metal rod failure could have been to blame.
"At this moment we're presuming that the top anchor bolts have come loose," he said.
A possibility being explored was that the bolts holding the metal piece suspending these panels had become aged, Satoshi Noguchi, an official with the highway operator, told the Associated Press news agency.
Recovery work has now been suspended at Sasago while the roof is reinforced.
Chief Cabinet Secretary Osamu Fujimura told a news conference on Monday: "The prime minister ordered the transport ministry to put the utmost efforts to rescue victims, to quickly investigate the cause of the accident and to establish measures to prevent similar accidents and to provide a counselling service to victims."
Rescue crews finally began bringing the bodies of the nine dead out of the tunnel on Monday morning.
Some were reported to have been so badly burned they would take days to identify.
Three charred and smashed vehicles could also be seen being pulled from the tunnel's mouth, our correspondent says.
Among the dead was a truck driver who had on Sunday called his company from his mobile phone saying he was trapped.
Five bodies were also recovered from a van. They were identified as three men and two women, all in their 20s and from Tokyo, Kyodo news agency reported. Another woman, 28, who had been in the vehicle survived.
Three bodies were found in another car.
Yamanashi prefectural police spokesman Yoshihiro Seto told the Associated Press news agency it could not be ruled out that more bodies or survivors could be found, but that the possibility was low.
The twin-bore Sasago tunnel on the Chuo Expressway in Yamanashi prefecture is one of the longest in Japan at 4.3km (2.7 miles).
Both sections will remain closed indefinitely.
In 1996, 20 people were killed when a tunnel in Hokkaido, northern Japan, collapsed and falling boulders crushed cars and a bus.