The Home Office has confirmed that a man staying at the Manston migrant processing centre has died.
A post-mortem examination is due to be carried out to determine his cause of death.
He died in hospital on Saturday morning after “becoming unwell”.
It is understood that he arrived in the UK as part of a small boat crossing on November 12, and was taken ill on Friday evening.
Efforts are under way to inform the man’s next of kin.
The small boats crisis has dominated headlines over the past few weeks, with ministers under fire for overcrowding chaos at the holding centre in Kent.
A statement posted on Twitter by the Home Office said: “We express our heartfelt condolences to all those affected.
“We take the safety of those in our care extremely seriously and are profoundly saddened by this event."
A Home Office spokesperson said there was “no evidence at this stage to suggest that this tragic death was caused by an infectious disease”.
They added: “We take the safety and welfare of those in our care extremely seriously and provide 24/7 health facilities with trained medical staff at Manston.”
At one point as many as 4,000 people were being detained at the site, which is designed to hold just 1,600.
This number later dropped to within capacity.
Asylum seekers are meant to be at Manston for only short periods of time while undergoing security and identity checks, before being moved to the Home Office’s asylum accommodation.
Some people have been held for longer periods due to a lack of alternative accommodation, with concerns raised over poor conditions.
Shadow home secretary Yvette Cooper said there will need to be a “full investigation” into the incident.
The Labour MP said: “We send deepest condolences to the family of the man who has died after staying at Manston.
“There will need to be a full investigation into what has happened in this tragic case.”
Enver Solomon, chief executive of the Refugee Council, said: “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.
“It is vital that a thorough and speedy investigation takes place to understand what happened and whether all the necessary procedures were followed.”