Horrific photos show the moment the Siberian big cat pounced on the woman as she tried to feed it at the Russian tourist attraction in Kaliningrad.
The images showed the woman lying on her back as the tiger pinned her to the ground, closing in for the kill.
Some visitors picked up a table and chairs from a nearby cafe, hurling it towards the animal in a bid to distract it.
Others began screaming and shouting as the 15-year-old male tiger named Typhoon, carried on its assault.
One witness described how the woman began screaming as she desperately tried to fight off the beast.
The zookeeper managed to flee when the tiger became distracted by the crowds.
With no other staff in sight, it was also up to the visitors to call for an ambulance.
She has since been taken to hospital and, miraculously, is expected to survive.
A visitor said: “The girl’s face face was bleeding.
“She screamed and tried to fight off the animal.”
It is thought the tiger had managed to slip away from a secure area in its compound, catching the zookeeper by surprise.
A zoo spokesman said: “The animal entered the enclosure when the keeper was there. The tiger attacked the human.
“Visitors with their shouting, stones and other improvisation managed to distract the animal.
“This allowed the zoo employee to hide in a back room.”
When zoo staff did arrive they managed to shoot the animal with a sedative.
A local health ministry spokesman said: “The patient was delivered to the hospital with multiple wounds to the body and limbs.
“She is conscious, her condition is assessed as stable but critical.
“There is no threat to her life.”
The Siberian tiger was born in 2001 at Chelyabinsk Zoo and later moved to the tourist attraction in Kaliningrad.
In the wild sSiberian tigers – a critically endangered species and the most dangerous big cat in the world – have a life expectancy of 15 years.
A member of zoo staff said: ”Typhoon has never before shown any aggression to zoo staff.”
But they said today the animal had been “bad-tempered” and “aggressive”.