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At least 68 migrants  — including two pregnant women — have been discovered packed into shipping containers at a port near London.

The East of England Ambulance Service said they had been called just after 10pm on Thursday night, amid reports of the discovery at Harwich International Port in Essex. 

It is believed that the migrants were spread between four separate trucks, and four Polish truck drivers have since been arrested, according to the London Evening Standard.

In a statement, the ambulance service said the migrants were feeling faint and were suffering from abdominal and chest pains. Seven people — including both pregnant women — were taken to Colchester General Hospital.

Related: Italy’s Mediterranean Mass Grave: Europe or Die

However, none are believed to be in a life-threatening or serious condition.

The remaining 61 migrants were turned over to UK border authorities.

Matthew Broad, of the East of England Ambulance Service, told the BBC that Thursday’s events had a “similar pattern” to other incidents.

“We have experience of dealing with this in Essex, and one of the things we were concerned about was the length of time they’d been in there,” he said.

Related: The Number of Migrants Trying to Reach Europe via Greece Has Surged by 500 Percent

Image via Wikipedia

The Associated Press contributed to this report.