A watchdog has described "wretched" conditions at a migrant processing centre which he warned has already passed the point of being unsafe.
Chief inspector of borders and immigration David Neal told MPs he was left "speechless" by what he saw at the Manston Airport site in Kent, prompting him to write to the home secretary with his concerns.
Migrants are meant to be held at the short-term holding facility, which opened in January, for 24 hours while they undergo checks before being moved into immigration detention centres or asylum accommodation - currently hotels.
The Commons Home Affairs Committee heard the site was already "outstripping" capacity.
It was originally meant to hold between 1,000 and 1,600 people but Mr Neal said there were 2,800 people at the site when he visited on Monday, with more due to arrive.
He said: "The numbers that have been described are clearly outstripping the capacity of the site."
The lack of officers and guards to match the number of people was "sufficiently alarming" he said, adding: "When I discovered that I was frankly speechless and I'm not someone who is normally speechless."
Describing the "pretty wretched conditions" he saw, Mr Neal said: "I spoke to an Afghan family who had been in a marquee for 32 days. So that's in a marquee ... with a kit mats on the floor, with blankets, for 32 days."
Speaking to the committee on Wednesday, he said: "I was very concerned about Manson when I visited on Monday. As concerned, perhaps, as I've ever been about anything over the recent years.
"It's a really dangerous situation. It's failing to address vulnerability ...There are risks there in terms of fire, in terms of disorder, in terms of medical and infection."
He said it's "absolutely inevitable in any form of detention setting that there could be fights that escalate. I think it's extremely concerning."
Mr Neal said there was a "creeping lack of ambition from the Home Office" over Manston.
When asked at what point the site ceases to be a place that is safe and can be run properly, Mr Neal told MPs: "I think we have passed that point.
"If there's nearly two and a half thousand people who aren't guarded by appropriately trained people, it's an extraordinary number. There's no prison in the country that's that big."
A small number of cases of diphtheria - a highly contagious infection which can prove fatal if not treated quickly - have been reported on the site over the last two months.
But Mr Neal said he understood it was only four incidents out of a population of 11,000 passing through the site and that the medical facilities there had "improved."