RIOT police were rushed to an immigration detention centre after an alleged armed mob caused a disturbance during a power cut.
The group of detainees were said to be armed with "various weaponry" as the incident unfolded at the London centre overnight.
The Home Office said the disturbance at the Harmondsworth detention centre, near Heathrow Airport, broke out after a power cut.
The Metropolitan Police were rushed to the centre around 8pm last night and still remained there more than 12 hours later.
Power had still not been restored at 9am.
But, a man inside the centre said detainees had been without power for far longer - and they were clueless as to what was happening.
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The detainee, who is unnamed, told : “I’ve not had any medication for nearly two days, I can’t function I’m in pain, I need it … my voice is gone from shouting ‘officer, officer, officer help us’.
“People are banging on the doors, they're terrified, I’m afraid for my life.”
The man claimed he had not seen an officer since 1.30am.
He said as they don't have power, they also don't have running water, adding: "We can’t flush the toilets, we don’t know what to do, the manager told us to ‘s*** in the bag’.”
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The man claimed he went out to the courtyard last night and ended up being locked out there with 50 people until about 1.30am.
He said that when the detainees were allowed back in, one-by-one, he noticed toilet roll and bins had been thrown around the building.
The detainee said: "We were left out until half past one in the morning and then one by one they took us in and locked us up in our cells.
“But there was nobody here all night. They abandoned us. There’s still no power or running water this morning I don’t know what to do."
The man's claims are a stark contrast to what officials have said so far.
In a statement, the Home Office said: "There has been a power outage at Harmondsworth immigration removal centre, and work is currently underway to resolve this issue.
There’s still no power or running water this morning I don’t know what to do.
Detainee
"We are aware of a disturbance at the centre and the appropriate authorities have been notified and are on scene.
"The welfare and safety of staff and individuals detained at Harmondsworth is our key priority."
The Metropolitan Police service and HM Prison Service were still at the scene around 10am.
A Home Office spokesman also told the PA news agency: "A group of detainees left their rooms and went out into the courtyard area armed with various weaponry.
"Territorial Support Police were sent to the scene, and the power is still off."
They added no one had been injured and that none of the detainees had left the premises.
Met Police told The Sun Online: “Police officers have been providing support to staff dealing with a disturbance at the Harmondsworth immigration removal centre.
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“Met officers attended the location at approximately 19:45hrs on Friday, 4 November.
“Officers remain at the location.”