Thousands of flights in and out of French airports were cancelled Wednesday as a strike by air traffic controllers intensified just hours before a nationwide rail strike was due to start.

With nearly 100 percent of air controllers following a call from unions to walk out over plans to create a single European airspace, up to three in four flights from the country's busiest airports were grounded.

Worst affected were Orly and Charles de Gaulle, the two Paris hubs, and Nice, the main airport for the French Riviera.

The cancellations affected mainly short-haul flights within France and to and from other European countries. Air France said it was hopeful of maintaining all its long-haul flights.

British Airways, easyJet and Ireland's Ryanair warned passengers that flights crossing French airspace were also subject to delays and cancellations.

France's civil aviation authority, the DGAC, said that 1,800 flights, just under a quarter of the weekday average, had been cancelled in anticipation of a second day of strike action.

But because of what it described as an "exceptional strike movement followed by almost 100 percent of air controllers", it had no option but to tell airlines to make further, last-minute cancellations, disrupting the plans of thousands of travellers.

Airlines operating from Charles de Gaulle, Orly, Beauvais, Lyon, Nice, Marseille, Toulouse and Bordeaux airports were being asked to cut a further 25 percent of their flights, the DGAC said, warning travellers to double-check that their flights were still operating before leaving for the airport.

A number of smaller regional airports -- Figari on Corsica, Montpellier, Perpignan, Angouleme and Agen -- were closed altogether.

The French air traffic controllers' strike coincided with work-to-rule protests in a number of other countries over the European Commission's proposals to create a single European airspace that, according to the EU executive, will cut costs, reduce pollution and increase safety.

French unions have denounced the move as back-door liberalisation of the sector which they say will lead to job losses and poorer working conditions.

France has asked Brussels to review the plans, a move which prompted the unions to cancel a third day of strike action that had been scheduled for Thursday, when more than half of France's trains will not be operating.

On average only four in 10 scheduled services on high-speed TGV or regional rail lines will be maintained as a result of a strike by rail workers that was due to begin on Wednesday at 7:00 pm (1700 GMT) and continue until Friday morning.

Eurostar services from Paris to London and high-speed links to Belgium, The Netherlands and Germany were not expected to affected by the strike but one in two trains to Switzerland and one in three to Italy were set to be cancelled.

Some commuter trains in the Paris region will also be affected, including the line that serves the two airports.

Unions have called the strike over government plans to create a new state-owned rail company which will incorporate both SNCF, the company that operates rail services, and RFF, the company that maintains the rail network, while still keeping the two branches separate.

Executives say the reform will make the railways run better at no additional cost to the taxpayer. Unions fear it will lead to the current system being dismantled.