UPDATE 3PM: Superintendent Greg Moore said the injured keeper, Jennifer Brown, was an experienced staff member.
He said police would work with the zoo to improve safety protocols.
"Understandably it's had a big impact on the staff - it's a small zoo and the staff are tight-knit," he said.
"And full credit to them for following their training to assist their colleague."
Supt Moore said he couldn't say whether the lions involved would be put down.
UPDATE 12.32PM: Inspector Faye Stockman, Duty Operations Manager, NSW Ambulance has addressed the media.
"This is one of the worst jobs I have ever experienced - I have never come across a job like this in my career," she said.
"It was absolutely harrowing. It is an incredibly dangerous situations, both for the patient and the paramedics."
"Being the first to walk into the enclosure was one of the most frightening experiences - we literally had to walk into a lion's den
"The attack was extremely vicious and paramedics found the woman with severe injuries.
"We are trained to deal with extreme or unusual situations, however, we do have support services available to us."
UPDATE 12.26PM: NSW Police Media have issues a statement about the incident.
"A woman has been airlifted to hospital after being attacked by two lions at a zoo on the South Coast today," it said.
"A 35-year-old woman was treated at the scene by NSW Ambulance paramedics for head and neck injuries, before being airlifted to St George Hospital in a critical but stable condition.
"Police have been told the woman was cleaning the enclosure at the time.
"Officers from South Coast Police District established a crime scene and commenced inquiries into the circumstances surrounding the incident."
UPDATE 12.08pm: NSW Ambulance have confirmed the woman has been taken by helicopter to St George Hospital. She is in a critical condition.
It is understood she was in an enclosure with two two-year-old lions at the time of the attack.
UPDATE 11.42AM: Ambulance media have confirmed the injuries were the result of a lion attack. The woman is in a critical condition. Multiple ambulance crews are on scene.
It is understood the woman is being treated on scene and the ambulance helicopter has not left yet.
A helicopter is on its way to Nowra after a keeper at Shoalhaven Zoo was reported to be unconscious with neck and facial injuries.
A NSW Ambulance spokesperson confirmed they were called just before 10.20am on Friday, May 29.
"There are reports of an unconscious zookeeper in the lion enclosure," the spokesperson said.
"The 35-year-old woman sounds like she has neck and facial injuries."
Several ambulance crews are already on the scene. More information to come.
The zoo has been part of the Shoalhaven for almost 50 years. Originally a wildlife park, in 2011 it changed it's name to the Shoalhaven Zoo to reflect the increased number of exotic animals on display, alongside native wildlife.
In 2014 a crocodile handler was rushed to Shoalhaven Hospital from the zoo, after a crocodile grabbed him by the hand and dragged him into the water during a feeding demonstration.
The handler recovered in a Sydney hospital.