PARIS (AP) - Paris commuters crammed into the city's only two working Metro lines as labour strikes over pension reforms crippled France's train services for an eighth day.

Tensions flared in several parts of the country. Police fired tear gas on Thursday morning (Dec 12) at protesters in the western city of Nantes, and protesters set vehicles on fire in the Mediterranean port city of Marseille.

Unions have flatly rejected fresh proposals by the government of President Emmanuel Macron to stagger the roll-out of a plan that would require France's youngest workers - people born after 1974 - to stay on the job until the age of 64 to get full pensions instead of age 62.

"No Christmas break unless the government comes to its senses," Laurent Brun of the General Work Confederation union, warned on Thursday.

The unions' dismissal of the proposal the government made on Wednesday signals that labour leaders were serious when they billed the strikes as "unlimited".

The strikes threaten to mirror similar ones in 1995 that lasted over three weeks, led to the ouster Prime Minister Alain Juppe and ended with proposed pension reforms being scrapped. The 1995 strikes were themselves compared in scale to the seismic events of May 1968, when France reached the brink of revolution.

Though Parisians have been adversely affected since they rely the most on public transportation, other parts of France have experienced less aggravation and the striking workers have enjoyed widespread public support, according to polls.

The mood among the public remains strained but understanding.

"I totally understand why people are on strike... Obviously, everyone is affected by the pension reform," London-Paris commuter Nicolas Lipitei said on Thursday.

"(But) I think there should be better provisions to accommodate getting to work. There's a huge impact on the economy, a huge impact of people's life in general," he added.

Many French people and the unions leading the strikes fear the new system will force people to work longer for smaller pensions.

The government said the changes would ensure the pension system is "fair and sustainable" in the face of a growing population with a record number of people over age 90.