Sixteen people have been discovered in a sealed trailer on a ferry sailing from France to the Republic of Ireland.

Operator Stena Line said a member of staff had heard banging on the inside of the container.

Ian Hampton said: “During the Stena Horizon's 9pm sailing from Cherbourg, France, to Rosslare in the Republic of Ireland on Wednesday, one of our employees during a routine inspection discovered 16 people in a sealed trailer on the vehicle deck.

“All the individuals are reported to be in good health and have been moved to a private passenger lounge on the ship where their wellbeing is the focus of our employees.

“Stena Line has alerted security and immigration officials in Rosslare so as the necessary arrangements can be made for the group on the vessel's arrival."

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Ambulances and police officers met the ferry as it docked on Thursday afternoon.

Irish police said: “An Garda Siochana are now investigating all the circumstances of this incident.

“The articulated truck involved in this incident has been detained.

“The driver and the owners of the articulated vehicle are assisting An Garda Siochana with our inquiries.”

The force said all the individuals appeared in good health and were receiving medical assessments after arrival at Rosslare, one of Ireland's main sea ports for passengers and freight.

It added: “Garda Immigration Officers attached to Wexford Garda Station, supported by the Garda National Immigration Bureau will carry out an assessment on the immigration status of all the persons.”

Taoiseach Leo Varadkar told broadcaster RTE: “Of course our initial response will be a humanitarian one, to make sure those people are well and that their health is good.

”After that of course there will need to be a response that involves the gardai, because as you know human trafficking is illegal, and we'll need to see what happens with the people who come ashore.“

The incident came amid continued attempts by human smugglers to move people from France to the British Isles.

The past year has seen a dramatic increase in attempted crossings by dinghies in the English Channel, prompting increased security along the French coast.

Smugglers have also used lorry trailers, including one where 39 Vietnamese people were found dead in Essex in October.

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On Tuesday, 25 stowaways were found in a refrigerated container on a cargo ship sailing from the Netherlands to Felixtowe.

The vessel was returned to Vlaardingen and given medical care.

Last year, the National Crime Agency (NCA) told The Independent that smugglers were using Ireland as a route to get migrants into the UK via the Schengen zone.

Officials were concerned about an increase in the number of gangs found to be working through the common travel area, where counterfeit passports have been used in the past.

Passports are not currently required for British and Irish citizens travelling between the two countries, and although air and sea carriers say they require some form of identification, documents are not always checked.

Tom Dowdall, deputy director of the NCA who leads on human trafficking, said organised crime groups had been “changing their modus operandi”.

“People from eastern Europe and further afield are coming into the UK via the common travel area through the Republic of Ireland,” he said.

“Some are flying into Ireland and travelling into the UK by air or ferry, and we have also seen coaches going to Ireland.”​

The NCA said it was also aware of groups who exploit the common travel area by giving illegal migrants false evidence of a history of living in Ireland, and therefore allowing them to enter Britain.

Mr Dowdall said that the main route for clandestine arrival was sea ports in southern England.