The accident occurred at around 8.40 am on a stretch of line between Miramas and Marseille centre, in the northern 16th arrondissement of the Meditterranean city, according to train operator SNCF.
According to initial reports the train collided with a crane on top of the vehicle, which caused the crane to collapse and embed itself into one of the train's carriages. The driver of the train managed to escape unhurt but was left in shock, French media reported.
The truck-driver, aged in his 40s, was more seriously injured and evacuated to a nearby hospital, where he is not reported to be in a life-threatening condition, according to regional daily La Provence.
Of the 75 passengers on board, 31 were injured, with the vast majority suffering bruises and shock from the sudden impact of the crash. They were transported by bus and other non-emergency means to a local hospital, according to reports by La Provence and French television TF1.
One passenger described two impacts - one from the initial collision between the train and construction vehicle, and a second from the collapsed crane entering the train's first carriage.
"One woman found herself with the crane practically at her knees. She thought she was going to die," the passenger was quoted as saying by La Provence.
Another testified to the frightening ordeal. "Some people were crying, and others were in shock. I was on a fold-up seat, so [upon impact] I slumped to the ground, and hurt my wrists."
Speculation over the cause of the accident continued on Tuesday afternoon, with the RFF rail company (Réseau ferré de France) claiming that at the time of the crash, traffic signals at the level crossing were working properly.
The company also claimed that barriers at the crossing were fully functional, and that the train tracks had recently been changed, according to TF1.
The local police's criminal and safety division is pursuing the possibility that the driver of the truck was on the phone at the time of the collision, after allegedly finding his mobile phone close to the scene of the crash, according to La Provence.