France has accused Italy of abusing Europe's visa-free border pact by issuing permits to migrants [GALLO/GETTY]

Hundreds of Tunisian migrants have assembled in Rome's main train station waiting for trains to the French border - some of the thousands believed to be on the move towards France.

"Every day there are hundreds more arriving," said Dorsaf Yacoubi, 18, an Italian student volunteer of Tunisian origin who handed out ready-meals to the migrants from the back of a van as passing tourists and police watched on Thursday.

Numbers at Termini station shifted during the day as the Tunisians arrived on some trains and left on others but there were around 200 at lunchtime.

The migrants were given free train tickets by officials to take them to Ventimiglia - the Italian town on the border with France that has been at the centre of a diplomatic dispute between Italy and France in recent days.

Not all have tickets however.

"It's not the police that stop them. When they take trains, ticket inspectors come and because they don't have a ticket, they call the police," Saidi Maha, volunteer at Termini Station, told Al Jazeera.

France has accused Italy of abusing Europe's visa-free border agreement Schengen by issuing temporary residence permits and travel documents to the migrants knowing that the French-speaking Tunisians are headed for France.

The free tickets are being provided by Italy's civil protection agency.

"Whenever homeless immigrants arrive at the station, they have to be taken immediately out of Rome," Rome mayor Gianni Alemanno said earlier.

"We will ensure that Rome doesn't become the end point of an uncontrolled wave of migration," he said.

More than 20,000 Tunisian migrants have arrived on Italian shores from Tunisia, complaining that the uprising that toppled president Zine El Abidine Ben Ali in January has failed to bring economic progress to their homeland.