French officials say that two women have been killed in the attack by a man with a knife at Marseille's main train station, including one whose throat was slit.
The officials say soldiers then fatally shot the attacker. Police have evacuated the Saint Charles station, with officers and soldiers taking up positions outside.
The officials spoke on condition of anonymity because they weren't authorized to discuss an ongoing investigation.
The Paris prosecutors' office says that a counter-terrorism probe has been opened, but no motive for the attack has been immediately given.
France's President Emmanuel Macron says he is "deeply outraged" by the "barbarous" attack.
Macron also paid tribute to the French soldiers assigned to domestic security who the president said in a tweet responded with cool heads and efficiency.
The French government this month decided to maintain the military force of 7,000 soldiers that was created to protect sensitive sites after the deadly extremist attacks of 2015
Prime minister Edouard Philippe also praised the soldiers who shot the suspect and stopped the "killing frenzy"
He expressed condolences to the victims' families and concern for Marseille residents.