Thousands of extra passengers swamped Eurostar London-Paris train services on Friday as the cloud of ash from an Icelandic volcano hit flights across Europe.
With airports across northern France closed until at least late Friday, international travellers rushed to find any alternative means of transport.
The Eurostar cross-Channel rail service laid on three extra Paris-London trains but places rapidly filled up and queues of passengers built up at the Gare du Nord station in Paris.
The company said 10,000 more travellers than usual had attempted to book Eurostar seats out of Paris on Friday, almost a third more than would normally have been expected.
"We've never seen so many passengers on such a day, when normally we'd transport between 26,000 and 28,000 people," said a Eurostar spokeswoman.
"We've seen a strong increase in interest since yesterday, as passengers seek alternative solutions," she added, warning passengers without tickets or reservations not to bother turning up.
A small number of flights were allowed to land at Charles de Gaulle and Orly, the two main Paris airports, between noon (1000 GMT) and 4:00 pm (1400 GMT), the DGAC civil aviation authority said.
"This opening remains too short to organise new turn-arounds, so it will be limited to arrivals," the agency said in a statement.
At Charles de Gaulle, France's main international hub, passengers slept on the benches of cafes or gathered in confused groups.
"We haven't had any news since last night. Our flight was expected at one o'clock, but it seems to have been cancelled," complained Elisabeth Lindley, trying to get back to Manchester, England.
"We heard that the flights were suspended, but I'm not going north, we're going south, so I thought I could take the plane," sighed Fatima, taking her granddaughter to Casablanca, Morocco, and stranded since dawn.
The state weather forecaster Meteo France said that the ash particles were moving southeast slowly across France from the north towards a line running roughly between the eastern town of Besancon and the western city of Nantes.
Meteo France expert Emmanuel Bocrie said that the ash could not really be called a "cloud" over France as the particles were diluted in the atmosphere and not really visible, while still presenting a danger to air transport.
Within France, a strike on the national network forced the cancellation of one high-speed TGV in 10, a fifth of regional trains and more than a third of local services, operator SNCF said.
Experts have warned the fallout from the Eyjafjallajokull volcano in southeast Iceland could take several days to clear.