France's main airport, Charles de Gaulle, has enough fuel to last only a few days, the transport ministry has warned amid strikes against government plans to raise the retirement age.
A ministry spokesman said officials were working to restore aviation fuel supplies. Economy Minister Christine Lagarde urged people "not to panic".
Oil refineries and fuel depots have been hit by the latest strikes.
Meanwhile unions are holding fresh mass protests over the pension plan.
On Saturday thousands of students have joined a fifth day of demonstrations in less than six weeks. Unions have called for more than 200 marches nationwide.
Police in Paris said 20,000 people were taking part in Saturday's protest when it started, shortly after 1500 local (1300 GMT), compared to 50,000 on 2 October, the last Saturday of protests.
Trapil, the company that operates the fuel pipeline to the Paris airports, told French media on Friday that supplies had stopped and that Roissy-Charles de Gaulle could run out of fuel as early as next week.
On Saturday a transport ministry spokesman confirmed to the AFP news agency that reserves would last until late on Monday or Tuesday.
But he said the pipeline was now working intermittently, adding: "We are exploring possible solutions to supply the airport [at Roissy]. We are confident."
All 12 oil refineries in France have been hit by the strikes. Ten have shut down or are in the process of closing.
A number of fuel depots have been blockaded.
Officials have insisted that France has enough fuel to see out the industrial action. On Saturday Ms Lagarde said: "There is no reason to panic over this... I am sure that we will unblock the situation through intelligent social dialogue."
However, some 10% of filling stations have run out of petrol and panic buying has broken out in some areas.
Meanwhile more than 200 marches nationwide are due to take place on Saturday. The protesters are opposed to President Nicolas Sarkozy's plan to raise the minimum retirement age from 60 to 62, and from 65 to 67 for a full state pension.
More than a million people took to the streets in the latest 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.
A sixth day of nationwide strikes and protests is planned for Tuesday 19 October.
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 of those questioned said they would support it.
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.
The pension reforms have already been approved by the National Assembly, the lower house of the French parliament.
The Senate has endorsed the key articles on raising the retirement age, and is due to vote on the full text on 20 October.