The four animals, one adult and four cubs, were seen outside Taronga Zoo’s exhibit on Wednesday at 6:30 p.m. (2:30 GMT Tuesday).
A zoo spokesman stated that although one cub was required to be calmed, all the lions were released within minutes. Nobody was hurt.
The escape is still unsolved.
Simon Duffy, the zoo’s executive director, said it was a “significant incident” and that it would be investigated.
According to him, the lions had entered an area that was “close” to their exhibit. It was about 100m away from the place where guests were staying overnight at the zoo. At the time, the main zoo was closed.
He stated, “The lions did not exit Taronga Zoo or that adjacent area at any time.”
Duffy said that the area was enclosed by a 6-foot fence, which is used to keep people from a safe distance. The perimeter fence also protected the entire zoo.
The zoo stated that CCTV footage showed that the alarm was raised by the keeper within 10 minutes of the escape.
According to Mr Duffy, staff quickly responded to move everyone on the site to safer locations. Four of the four lions “calmly returned” to their enclosure.
Mr Duffy stated that the lion exhibit will be closed until further inspections are done to ensure it is “100% safe”.
It is rare for animals to escape from Australian zoos.
A lioness that had escaped from its enclosure at Mogo Zoo in south Sydney in 2009 was shot dead due to the danger it posed for the public.
