People arriving into Northern Ireland and the rest of the UK, from France, the Netherlands, and a number of other countries, are required to self-isolate for 14 days because of rising numbers of coronavirus cases.
The quarantine, which came into effect at 4am, also applies to those coming from Malta, Monaco, the Turks & Caicos Islands, and Aruba.
France continues to register rises in the number of new cases of coronavirus with the numbers in recent days similar to those in mid-April, when the country was still in lockdown.
The French government has declared Paris, Marseilles, and its surrounding area, red zones.
Tens of thousands of UK tourists in France rushed home before quarantine restrictions were imposed.
Travellers scrambled for plane, train or ferry tickets costing hundreds of euro.
The UK government insisted it had taken "a practical approach" to the new restrictions.
Eurotunnel Le Shuttle, the train service which carries vehicles through the Channel Tunnel, was fully booked yesterday.
A spokesman said 12,000 people tried to book tickets in the hour after the new rules were announced at around 10pm on Thursday, compared with just hundreds normally.
Some air fares were more than six times more expensive than normal.
British Airways was selling tickets for a flight from Paris to London Heathrow on Friday night costing €499.
The same journey today could be made with the airline for just €73.
The cheapest ticket on a Eurostar train from Paris to London was €232, compared with €182 on Saturday.
Travellers in the south of France and the Netherlands faced a struggle getting back to the UK yesterday as many direct fights were sold out.
Dyan Crowther, chief executive of the HS1 high-speed London to Channel Tunnel rail link, said it was "heartbreaking" seeing families having to cancel holiday plans and spend hundreds of pounds dashing home to beat quarantine.
A spokeswoman for travel trade organisation, Abta, said the UK government's quarantine policy will "result in livelihoods being lost unless it can step in with tailored support for the travel industry".
The Joint Biosecurity Centre and Public Health England detected a significant change in Covid-19 risk in all six destinations for which quarantine restrictions were imposed.
