A fifth day of protests in France against proposed pension reforms brought 825,000 people on to the streets, police said, although unions put the figure at 2.5m to 3m.
The government wants to raise the retirement age from 60 to 62 and the full state pension age from 65 to 67.
Most oil refineries have been hit by strike action, causing fuel shortages at some airports and filling stations.
A further day of strikes is scheduled for Tuesday.
The pension reforms have already been approved by the National Assembly, the lower house of the French parliament.
The upper house, the Senate, has endorsed the key articles on raising the retirement age, and is due to vote on the full text on Wednesday.
Public and private sector workers took part in strikes on Saturday across France, in cities including Paris, Marseille, Lyon, Bordeaux, Lille and Toulouse. Unions had called for more than 200 marches nationwide.
"We are not here to bring France to its knees and create a shortage, we are here to make ourselves heard," Christian Coste, of the CGT trade union, told the Associated Press.
A group of what the police described as anarchists operated on the fringes of the main demonstration, says the BBC's Hugh Schofield in Paris.
As the protest drew to a close, they began ransacking café terraces, breaking windows and setting fire to bins.
Some of them briefly occupied the Opera House at Bastille.
The clashes did not last long, but they are a reminder to the government and unions of how quickly things can get out of hand, our correspondent says.
All 12 refineries in mainland France have been affected by strike action. Ten have shut down or are in the process of closing. A number of fuel depots have been blockaded.
However, a pipeline supplying the two main airports in Paris, Charles de Gaulle and Orly, is now back in service. It was cut off by strike action, raising fears that Charles de Gaulle would run out of fuel by Tuesday.
France also has a strategic fuel reserve which holds up to three months of supplies.
However, some 10% of filling stations have run out of petrol and panic buying has broken out in some areas.
In Marseille, rubbish is piling up around the port amid a strike by bin collectors that has now lasted four days.
More than 300 high schools have been affected by strikes and blockades - about one in 15 across the country - as students have joined the pension protests in the past week.
Lorry drivers will decide on Monday whether to join the strikes.
More than one million people took to the streets in the previous national protest on Tuesday, according to police. Trade unions organisers said 3.5m had taken part.
The last weekend day of demonstrations was Saturday 2 October, when the numbers were about 900,000 according to police and 3m according to unions.
Seventy percent of people polled this week think the sporadic strikes will build into a national protest movement like the one in 1995, and over half said they would support it.
In 1995, three continual weeks of strikes by public and transport workers forced the government to abandon plans for economic reforms, including raising the retirement age.