Many people were feared dead and at least seven missing after 150 concrete panels fell from the roof of a tunnel on the main highway linking Tokyo with central Japan.
Efforts to rescue any survivors trapped inside the tunnel were hindered by heavy smoke after a vehicle caught fire inside Sasago Tunnel, about 80 km outside Tokyo.
Rescuers also temporarily suspended work due to fears of a further collapse. They were attempting to reach several vehicles believed buried in rubble, including a truck whose driver was trapped inside and had called his company for help.
The Fire and Disaster Management Agency issued a statement late Sunday saying five people were confirmed to have been in a car that burned, and at least one was in a truck. But officials said they could not confirm the exact number of people believed dead.
Executives for Central Japan Expressway Co. said the company was investigating why the concrete panels had given way.