Laura Miller, 43, was cleaning cages at Parkway Animal Hospital, Florida, on Thursday when the dog pounced, taking her underarm between its jaws and 'violently shaking her', according to the Bay County Sheriff's Office.
Two of the woman's colleagues ran to the scene and began kicking and hitting the animal until it released her from its grip.
The dog was locked in a cage but shortly after was sent to Animal Control, which is deciding whether or not to euthanise the animal.
Ms Miller was rushed to Bay Medical Center where doctors were forced to amputate what was left of her arm at the shoulder because it was so badly mauled.
The woman also suffered bites to her neck and upper torso.
'It was very bloody, there was blood everywhere,' sheriff's spokesman Ruth Corley told MailOnline.
'The workers said when they came into the kennels the dog had her in its grip and was violently shaking her. They had to fight the dog to have him let go of her.'
The woman, originally from Panama City with no family in the area, lost a lot of blood during the brutal attack and only late yesterday regained consciousness.
She was then able to give investigators a statement.
The pit bull had been at the boarding kennels for around nine days when the attack took place, at about 5pm.
Police said they didn't know why the dog, which had been well behaved during this and previous stays, turned vicious.
'At the moment, we don't know why the dog attacked her,' Ms Corley said
'Animal control took the dog immediately and have to determine whether the dog has a history of violence or if it has already been deemed vicious.'
The pit bull's owners, who were on holiday at the time of the mauling, could face criminal charges if it turns out they knew the animal was dangerous.
Owners of dogs known to be viscous are required to look after them in a certain way to protect the public.
(Daily Mail UK - July 21, 2012)