The death toll in Japan's tunnel collapse rose to nine on Monday.
Two people are also seriously injured when 110 metres long section of the tunnel's concrete ceiling panels fell onto cars.
Surveillance camera shows rescuers working inside the tunnel, while crushed cars get towed away.
An official from the highway operator said metal rods used to secure the concrete panels may have become loose.
(SOUNDBITE) (Japanese) NEXCO OTSUKI SAFETY SERVICE CENTER CHIEF, MOTOHIRO TAKAMISAWA, SAYING:
"At this moment we're presuming that the top anchor bolts have come loose."
NHK reported, the ceiling panels had not been repaired or reinforced since they were built in 1977, but they passed safety checks in September.
Japanese media reported that the authorities have ordered highway companies with similar concrete panels to have emergency inspections.