Japanese emergency officials discovered five bodies in a van, a body of a man in a cooler truck and three other bodies in a car, according to the website NHK English. Officials say 30 cars are involved.
The tunnel collapsed early Sunday morning, trapping vehicles as smoke from a fire inside initially prevented rescuers from approaching.
Video footage from cameras inside the tunnel, after the fire was extinguished, showed firefighters picking their way through concrete roof panels that collapsed onto vehicles inside the Sasago Tunnel, about 80 kilometres outside the city.
The Fire and Disaster Management Agency issued a statement Sunday saying five people were confirmed to have been in a car that burned inside the tunnel, and at least one other was in a truck.
The agency also said two people were confirmed injured, one of them moderately.
A woman who escaped from her rental car after it was trapped in the 4.3-kilometre-long tunnel told authorities she was unsure about the condition of five other people who had been in the vehicle with her.
Executives for Central Japan Expressway Co. said the company was investigating why the concrete panels had given way. A check of the tunnel's roof in September and October found nothing amiss, they told the Associated Press.
Approximately 150 panels fell from the roof, affecting about 110 metres of the tunnel.
Police vehicles, fire trucks and ambulances were massed outside the tunnel's entrance. A man who said he saw the collapse and alerted authorities to the emergency told NHK television he managed to escape after he was ordered to flee.
The roof and windows of another vehicle parked on the roadside outside the tunnel were crushed, and the injured occupants reportedly taken to a hospital.
The Sasago Tunnel, which opened in 1977, is one of many along Japan's mountainous landscape. It is widely used, with tens of thousands of cars likely passing through in a single weekend, according to local media.
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