Emergency services were called to Darling Downs Zoo in Pilton, south of Toowoomba, about 8.23am after the woman in her 50s was attacked from outside an enclosure by a captive-born female lion.

The zoo said in a statement the woman was not in the animal's enclosure when the attack took place and they have so far been unable to establish how the "tragic incident" unfolded.

"She has lost her arm. She is not an employee, a keeper or a zoo visitor," Darling Downs Zoo said in a message shared to Facebook.

"She is a much loved member of the zoo owners' family.

"She was not in it's enclosure. It was not hungry, skinny, taunted or tortured – it is a lion."

The zoo owners said the lion would not be put down and a full investigation had been launched by Workplace Health and Safety Queensland.

"It comes from a long line of captive born lions in Australia but it is still a lion – not a pet," the statement continued.

The woman was watching keepers in the enclosure when one of the animals attacked.

"The animal will definitely not be put down or punished in any way," Darling Downs Zoo said in a message shared to Facebook yesterday evening.

It also said the animal had not recently had cubs.

The zoo confirmed it will remain closed today and plans to reopen tomorrow.

Nationals leader David Littleproud said the attack would have been an "enormous shock" to fellow zoo staff.

He also encouraged locals to continue to attend the much-loved animal park.

"I express my sincere condolences to the woman involved in the events that unfolded at Darling Downs Zoo," Littleproud said.

"This is a horrific incident. It is a tragedy and a shock to not just staff at the zoo, but the entire community."

He added: "I encourage locals to continue to visit and enjoy the zoo, which will need support from the community during this difficult time."

The zoo said the woman was a longtime member of the zoo "family".

"This is something that she has done many, many times over the past 20 years," the zoo said on Facebook.

"She is well versed in safety protocols around potentially dangerous animals.

"Inexplicably, at this stage, one animal grabbed her by one arm and caused severe damage to it."

9News understands she was saved by the quick actions of an employee who used a belt to tie a tourniquet.

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