Nathalie Loiseau, the minister for European affairs, said it was correct that both trains and planes from the UK would be barred without an exit agreement.
If we reach no agreement this is what will happen, among other things, Ms Loiseau told an event in London.
The warning comes one week after a secret Treasury document acknowledged there were questions about rail access to the EU if there is a no-deal Brexit.
But No 10 refused to discuss what was meant by the reference on the Operation Yellowhammer document, photographed as a minister carried it into a Whitehall meeting.
The government has previously acknowledged that planes would be grounded without a post-Brexit agreement, while insisting the prospect was remote.
However, the UK’s attempts to prepare side deals with individual EU member states to avoid transport chaos, if they became unnecessary, earned a rebuke from Michel Barnier, the EU’s Brexit negotiator.
Rupa Huq, a Labour MP and supporter of the People’s Vote campaign, said: No-one voted for a Brexit that results in flights being grounded or the Eurotunnel being closed down, but that’s what the French Europe minister was warning about today.
The gap between the Brexit that was promised and the one that’s being delivered grows wider all the time.