At least seven people were missing and several feared dead after about 150 concrete panels fell from the roof of a tunnel on the main highway linking Tokyo with central Japan.
Efforts to rescue survivors trapped inside were hindered by heavy smoke after one vehicle caught fire inside the Sasago Tunnel, about 50 miles outside Tokyo.
Rescuers also temporarily suspended work because of fears of a further collapse.
They were attempting to reach at least several vehicles believed buried in the rubble, including a truck whose driver was trapped inside and had called his company for help.
“I could hear voices of people calling for help, but the fire was just too strong,” said a woman interviewed by public broadcaster NHK after she escaped from the tunnel.
The Fire and Disaster Management Agency said five people were confirmed to have been in a car that burned inside the tunnel, and at least one other was in a truck.