At least two people have been killed and multiple injured, according to French BFM TV.
Some victims are said to be seriously injured after the rampaging knifeman attacked.
A Reuters police source said the knifeman screamed “Allahu Akbar” meaning God is great, as he stabbed two people.
The French prosecutor has confirmed the attack at the Saint Charles station as he makes his way to the area.
Police have described it as an "ongoing" incident and asked people to avoid the area which has now been evacuated.
The mayor of Marseille reportedly said the "number of victims could have been higher" as the army swooped on the station.
France originally declared a state of emergency in the country after the November 2015 terror attacks in which 130 people were killed.
Multple attacks have rocked the nation including a horror Islamic State (ISIS) assault on Nice in which 84 were massacred on Bastille Day.
