French riot police have fired tear gas at striking train workers who hurled bottles and blocked traffic in anger over a bill to reform the state-run railway system.

A week-long strike by rail workers is heating up as the draft law goes to the lower house of parliament for debate.

Several hundred workers staged a protest near the National Assembly on Paris's Left Bank, waving red union flags.

The bill would pave the way to opening up the railways to competition, and opponents fear it will lead to job losses and safety problems.

The protesters blocked cars and tried to approach the parliament building, firing flares and throwing bottles. Officers responded with tear gas and wrestled a few protesters to the ground.

The bill would unite the SNCF train operator with the RFF railway network.

The government says the reform is needed to create a stronger structure for the railways, as France and other European countries gear up for full-scale railway liberalisation in coming years.

French television showed footage of protesters marching on to train tracks at Paris's busy Montparnasse station, which links travellers with cities across western and south-west France.

The strike began last Wednesday, and while only a minority of workers are taking part, it has disrupted travel on trains across France and on commuter lines.

About a third of trains were canceled nationwide today. The strike has not affected international lines such as the Eurostar train from Paris to London, but it has caused problems for international travellers using the commuter rail to and from Charles de Gaulle Airport.