According to local newspaper La Dêpeche, the car contained a 15-year-old boy and his parents and the boy died at the scene.
The 150m long suspension bridge had a weight limit, and initial reports suggested that a large lorry had driven onto it when it collapsed.
The head of the Haute-Garonne départment Georges Meric told AFP that three vehicles were caught in the bridge collapse, without saying what happened to the third.
Over 60 emergency workers were at the scene, he said, adding that an investigation would be carried out into the condition of the bridge.
Local authorities have urged people to stay away from the area and added that as a precaution the nearby Villemur suspension bridge has also been closed.
Comment: Update 19 Nov
French media reports that the driver of the large truck was found yesterday night at around 22:00 CET
A French senator has sounded the alarm, reminding people that, following the 2018 bridge collapse disaster in Genoa, Italy, he had published a report about the state of France's bridges. Around 25,000 of them - 10% of bridges in France - are in urgent need of repairs or complete replacement because they were built up to a century ago.