Iranian asylum seeker Reza Berati died and 77 others were injured in the February 16 to February 18 riots.
Chandra Osborne, who was working as a guard at the time, told the court there was chaos when detainees first broke out of the centre's Oscar compound about 7pm on February 16.
Ms Osborne, who is suing the federal government and security firm G4S, said she was ordered to stay as the single guard in the separate Charlie compound as the violence escalated.
In her evidence on Wednesday morning, Ms Osborne detailed an incident where Papua New Guinean guards attempted to scale the locked Charlie compound fence to attack her, yelling threats to kill her.
They were unsuccessful, she told the court, but their actions and ensuing chaos between the guards and detainees left her feeling terrified.
Throughout that first night of riots, Ms Osborne said there were at least 10 injured detainees brought to the Charlie compound with broken bones and bleeding.
After working until 4am, hours after she was meant to have finished, Ms Osborne said she was ordered to return back to the Charlie compound at 9am on February 17.
Ms Osborne gave evidence that the daytime was calm, but as the night returned, so did the violence.
She said while the nights blurred into each other, she remembered hearing gunshots, chanting and yelling, and seeing smoke throughout the centre.
Ms Osborne broke down in tears as she recalled returning to the staff quarters about 4am on February 18 to see several casualties being treated against a wall.
"I was so exhausted, I couldn't help," she told the court through tears.
Ms Osborne alleges the federal government and security firm G4S were warned about increasing violence but still put her at risk.
She is seeking compensation for loss of earnings after she allegedly suffered serious psychiatric injuries as a result of the riots and unsafe working environment.
Both the Commonwealth and G4S are disputing the allegations in the Supreme Court.
Ms Osborne's evidence will continue on Wednesday afternoon.
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