At least nine bodies have been found in a highway tunnel in central Japan after a portion of tunnel collapsed Sunday morning. 

Emergency officials found five bodies in a van, the body of one man in a cooler truck and three other bodies in a car in the passageway that links to Tokyo.

Officials at the Fire and Disaster Management Agency said it was not clear if there are any other victims.

Rescue efforts were suspended Monday local time as work was being done to reinforce the tunnel’s roof to prevent any more collapses.

About 30 vehicles were in the Sasago Tunnel when about 150 concrete panels, each nearly 10 centimetres thick, fell from the roof onto the main highway.

At least three vehicles were trapped under the rubble in the 4.7-kilometre passageway. The collapsed occurred midway through the tunnel, which complicated rescue efforts.

Emergency officials were also hampered by heavy smoke after two of the cars inside the tunnel caught on fire.

"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.

NHK reports that heavy machinery is being used to remove the concrete debris, which is scattered for more than 100 metres.

Executives for the Central Japan Expressway Co. said an investigation is underway to determine what caused the concrete panels to collapse. Inspections of the tunnel’s roof that took place in September and October found it was structurally sound.

Company officials said two others suffered minor injuries in the collapse.

Central Japan Expressway Co. president and CEO Takekazu Kaneko said that the organization was inspecting other tunnels of similar structure, including a parallel tunnel for traffic going in the opposite direction.

Both sections of the highway were shut down indefinitely.

The Sasago Tunnel, located about 80 kilometres outside of Tokyo, opened in 1977. It is one of many tunnels in the mountainous region.

With files from The Associated Press