NHK has learned that a portable battery charger may have caused a fatal fire last week at a lodging house in Kawasaki City near Tokyo.

Firefighters have found a charred portable charger in a room on the first floor of the lodging house, where they think the blaze likely started. Two men died in the fire.

The guest assigned to the room was not there at the time of the fire and told investigators the device had been left charging.

The National Institute of Technology and Evaluation, or NITE, says a portable battery charger could catch fire if it has a flaw inside or it is left in a hot place.

NITE notes that a component inside the charger can be broken if it falls on the ground or something heavy is put on it, but that this internal defect cannot be seen from outside.

The institute urges users not to leave the device unattended while recharging it and not to place it near anything combustible.

NITE also asks users not to leave chargers in direct sunlight or in hot places.