Sixty-eight people were found Thursday night locked inside a cargo container shipped to Harwich International Port in the United Kingdom that had arrived from the Netherlands. The container was reportedly on a ferry, operated by Sweden's Stena Line, from the town of Hook of Holland.

A port spokesman said the stowaways were found as part of a routine inspection, the BBC reported. The group comprised of 53 adults, including two pregnant women, and 15 children, from Afghanistan, China, Vietnam and Russia.

The case was reportedly handed over to the Border Force staff for investigation because it was related to immigration offense.

At least seven migrants were taken to a local hospital for treatment. 

"The patients who were taken to hospital were suffering from abdominal and chest pains and were feeling faint,” a spokesman for the East of England Ambulance Service said, according to the London Evening Standard. "None are in a life-threatening or serious condition. The remaining 61 were released to the UK Border Agency officials."

A representative of the U.K. home office reportedly said four Polish truck drivers were arrested in connection with the incident "on suspicion of facilitating illegal immigration."

“They have been taken to separate police stations and will now be questioned by the Home Office’s criminal investigations team while inquiries continue,” the official added, according to ITV.

This is not an isolated incident in the U.K. Last August, a group of 35 Afghan Sikh migrants were found in a container at Tilbury docks in Essex. One of the men was found dead inside the container.

In March, an inquest was opened after two Albanian migrants drowned while trying to swim back to the U.K. shore as they were being deported. The two had jumped off from the Stena Britannica ferry off Suffolk during a deportation from Essex on 26 Feb. 2013.

Border Force officer Giles Young had told the inquest: “We see a lot of these particular cases and the same people will turn up two or three times. We have individuals this year who are already on their second attempt and it is only March. The Dutch sometimes release them into Holland and they try again. It's a carousel system,” according to the Guardian.

The number of migrants attempting the desperate crossing into Europe has soared in recent years, as the crisis situation in countries across the Middle East and Africa prompted over 130,000 to arrive on European shores in 2014.