Cross-Channel ferry services have been disrupted due to a blockade at the Port of Calais.
Ferry movements at the French port were suspended due to industrial action by former MyFerryLink staff members.
Mayor of Calais Natacha Bouchart said she regretted that the port was being taken "hostage" and travellers are urged to contact their operator before setting off.
A Port of Dover spokesman said: "We will continue to monitor the situation closely in liaison with our ferry partners and the Port of Calais in order to resume normal operations as soon as possible."
Up to 2,000 British holidaymakers and other travellers are thought to be affected.
Workers are protesting the potential loss of 600 jobs caused by the sale of MyFerryLink, which provides services between Dover and Calais, according to the Daily Telegraph.
The Port of Calais has reopened after it was temporarily closed to allow two unexploded Second World War mines to be disarmed.
The main access to Calais Port (Rocade), all ferry check-in booths, the UK Border Force and French Border Control booths had been closed from 7am French time.
Cars arriving at the port were being diverted to a nearby sports hall until it reopened around seven hours later.
P&O Ferries, which runs services between Dover and the French port, tweeted that it would work to get waiting customers on the next available boats.
It later confirmed that all services between the two countries were operating on schedule and had spaces available.
Thirty-one stowaways had their hopes of entering the UK shattered after border officials found them hidden inside four UK-bound lorries at the Port of Calais.
A sniffer dog indicated there were people inside a Peterborough-bound Turkish-registered lorry and 12 Albanians were found among the cargo.
Officers using heartbeat monitors also discovered six Afghans hidden in a Polish-registered vehicle which was heading to Accrington, Lancashire, with its load of sofas.
A detector dog also led officers to find six Albanians hidden among nappies on a Czech-registered lorry bound for Lincolnshire.
The fourth discovery was in an Irish-registered lorry heading to the Republic of Ireland. A dog led officers to find seven people on board - three from Iran, two from Pakistan, one from Afghanistan and a Syrian.
All the stowaways were handed over to French border police.