LONDON — A man being held at a much-criticized center for migrants in Britain has died after falling sick, bringing renewed criticism to the Conservative government over its treatment of asylum-seekers.

The Home Office said a man who was staying at the Manston migrant center in southeast England died in a hospital on Saturday after “becoming unwell.”

Authorities are trying to contact next of kin of the man, who is believed to have arrived in England in a small boat on Nov. 12.

“We take the safety of those in our care extremely seriously and are profoundly saddened by this event,” the Home Office said. “A post-mortem examination will take place so it would not be appropriate to comment further at this time.”

It said there was “no evidence at this stage to suggest that this tragic death was caused by an infectious disease.”

Cases of diphtheria, scabies and other communicable diseases have been reported at Manston, where people who have arrived by boat across the English Channel are sent for security and identity checks before moving to longer-term accommodation.

A surge in arrivals and a bureaucratic backlog has seen people, including children, languishing for weeks. A facility intended to house at most 1,600 people had more than 4,000 occupants last month, after hundreds were moved there from another site that was firebombed by a far-right attacker. The number has since dropped.

Independent government inspectors who visited the site said they saw families sleeping on floors in prison-like conditions that presented fire and health hazards.

Enver Solomon, chief executive of the Refugee Council, called for “a thorough and speedy investigation” of the death.

“Every person in Manston must be looked after with the care and attention they need, so when a tragic death likes this takes place it is always a matter of serious concern,” he said.

The U.K. receives fewer asylum-seekers than many European nations, including Germany, France and Italy, but thousands of migrants from around the world travel to northern France each year in hopes of crossing the channel. Some want to reach the U.K. because they have friends or family there, others because they speak English or because it’s perceived to be easy to find work.

In recent years there’s been a sharp increase in the number of people attempting the journey in dinghies and other small craft as authorities have clamped down on other routes such as stowing away on buses or trucks.

More than 40,000 people have arrived in Britain after making the hazardous Channel trip so far this year, up from 28,000 in all of 2021 and 8,500 in 2020.

Dozens have died in the attempt, including 27 people almost exactly a year ago when a packed smuggling boat capsized.

The small-boat crossings are a longstanding source of friction between Britain and France. Last week the British government agreed to pay France 72.2 million euros ($75 million) in 2022-2023 in exchange for France increasing security patrols along the coast by 40%.

In another attempt to deter the crossings, Britain’s government has announced a controversial plan to send people who arrive in small boats on a one-way journey to Rwanda, to break the business model of smuggling gangs. Critics say the plan is immoral and impractical, and it is being challenged in the courts.