The agency has received at least eight reports of engine compartment fires in the small city cars.

The National Highway Traffic Safety Administration has opened an investigation into the Smart Fortwo after receiving several fire complaints.The agency has identified eight reports claiming the small city cars suffered catastrophic engine compartment fires. All involve vehicles from the 2008-2009 model years.

"All eight incidents involve severe fires that rapidly engulfed the vehicles," the NHTSA investigation documents note.

Six complaints claim the fires were preceded by smoke, check engine light illumination or unusual noise while driving. In the other two cases, the fires were not detected until the vehicles were stopped.

The agency will now complete a preliminary evaluation to determine if a deeper inquiry and engineering analysis are warranted. If the investigation leads to a recall, it could affect approximately 43,000 vehicles sold in the US market.