A "critical incident" was declared at the Port of Dover after 14 asylum seekers were found in a tanker on board a cross-Channel ferry.
They were discovered on P&O's Spirit of France vessel on Wednesday morning and seven are receiving medical attention, Port of Dover Police said.
None of those found was in a life-threatening condition and ferry services have not been affected by the alert at the Kent port's Eastern Docks.
A Port of Dover Police spokesman said: "The Port of Dover can confirm that a critical incident is under way concerning 14 asylum seekers found in a tanker on board P&O's Spirit of France.
"Emergency services are at the scene and are dealing with the situation in close co-operation with port staff.
"Seven of the asylum seekers are receiving medical attention but none are currently considered in a life-threatening condition.
"The port is still open and ferry services are currently unaffected."
Kent Fire and Rescue Service said it was called to deal with an incident at the port's Eastern Docks at 8.45am.
Six fire engines and some specialist equipment were sent to the scene and Kent Police also attended.
Kent Fire and Rescue Service later said: "Kent Fire and Rescue Service was called at 8.45am today to assist at an incident in Eastern Docks, Dover, concerning 14 asylum seekers found in a tanker on board P&O's Spirit of France.
"Six fire engines and some specialist equipment have been sent to the scene to assist with rescuing a number of people.
"Kent Police, SECAmb, the Border Control Agency and the HMRC are also in attendance and dealing with the situation in close co-operation with port staff.
"Seven of the asylum seekers are receiving medical attention but none are currently considered to be in a life-threatening condition."
A P&O spokeswoman said the company currently had no comment to make.
Examination of the tanker was continuing but police said a powder found on board was non-hazardous, the police spokeswoman added.
A SECAmb spokesman said two people were taken to the William Harvey Hospital in Ashford.
He said: "We didn't have any reports of anyone in a life-threatening condition but the people needed to be checked over, with some having minor breathing difficulties and chest pains.
"We sent a total of eight vehicles, of which three were ambulances."