The motive of the attack was not known, police sources told AFP. But one source said there was so far no indication of terrorism.
The stabbing struck at about 8pm on Wednesday in a busy district on the banks of the Garonne river.
One police source said the attack had "no terrorist connotation for the moment".
The source said it was likely to be "a brawl with an unknown motive".
Security concerns are high in France as Paris prepares to host the Olympic Games in July and August.
Wednesday's attack was the latest of several deadly stabbings to shock France in recent years.
On February 3rd, three people were injured in a knife attack at Paris's Gare de Lyon railway station. Police said a suspect with psychiatric problems was arrested in that case.
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