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Emergency services were called to the Port of Dover after reports of people found on board a vessel.
The ambulance service and police are supporting the Border Force after the discovery on Sunday.
A spokesman for the South East Coast Ambulance said they were called late yesterday evening to support Border Force with "an incident at Dover Western Docks".
They sent an ambulance team to attend and they remain on the scene.
This morning, emergency services including specialist paramedics and a fire service vehicle remained in attendance along the pier.
A spokesman for Kent Police said: "Kent Police officers are currently assisting Border Force colleagues in Dover after a number of suspected migrants were found on board a vessel."
A Home Office spokesman said: "Kent emergency services, supported by Border Force, were dealing with an incident at Dover where five individuals, who presented themselves at Moroccan nationals, were found on board a vessel destined for Dover.
"Four of the individuals were adults and one was a minor. They were all found to be fit and healthy with no medical issues.
"The vessel has now berthed and further searches are underway as a precautionary measure. This is an ongoing incident."
The Home Office has been approached for comment.