PARIS (AP) - French airport workers, teachers and others joined nationwide strikes on Tuesday (Dec 10) as unions cranked up pressure on the government to scrap changes to the national retirement system.

Police ordered shops and restaurants closed across a swath of Paris, fearing violence on the fringes of what government opponents hope is another mass march in the afternoon. At least 800,000 people turned out for demonstrations around France when the strike movement kicked off last Thursday.

Protests are also planned on Tuesday in other cities, as the strike pushes on into a sixth straight day.

Unions fear President Emmanuel Macron's retirement reform will force people to work longer for smaller pensions, even though the government says it won't raise the official retirement age of 62.

Only about a fifth of French trains ran normally on Tuesday, frustrating tourists who found train stations empty and trains cancelled, and most Paris subways were at a halt. The Paris region registered double the number of traffic jams at morning rush hour than on a normal day.

Overall, the number of striking workers is lower than last week but travellers' patience is wearing thin, as commuters struggle to squeeze on scarce regional trains to get to work.

Air France, the national carrier, said more than 25 per cent of its domestic traffic would be grounded on Tuesday by the strike, along with more than 10 per cent of its medium-range flights.