An Australian freshwater crocodile has been captured in a city creek thousands of kilometres south of its normal range, after sightings shocked onlookers at a suburban park.

The crocodile was first spotted in Ironbark Creek in Newcastle – about 100km north of Sydney – around midday on Saturday, by a group of teenagers.

Stephanie Kirsop, the mother of one of the teenagers, said when her son called her to relay the sighting, her initial reaction was: “This is a trick … it looks like a crocodile but that’s probably a log.”

“It took him about two hours to fully convince me to go down there and have a look,” she said. “I get there, I look and here’s this little crocodile swimming around in the water.”

The sighting occurred at Federal Park in Wallsend, close to a local pool and primary school.

Kirsop said she was met with initial disbelief when she contacted the wildlife rescue group Wires, and the Australian Reptile Park.

She also contacted New South Wales police who sent an officer to the park at about 4.30pm on Saturday. “Once that police officer saw that crocodile out swimming in the water, that’s when everything started going a bit quicker,” Kirsop said.

A team of crocodile handlers, led by Billy Collett of the Australian Reptile Park, captured the freshwater crocodile on Sunday night, after multiple attempts on Saturday night and Sunday morning.

“We didn’t have a boat [on Saturday], so the [State Emergency Service] dropped us off a rescue raft,” Collett said. “We paddled that down but it was just too slow to get enough to jump without him spooking.”

Collett’s team returned on Sunday with a motored tinnie, finding the croc in the evening near wetlands approximately 3km downstream from where it was first spotted. “I just sent it off the nose of the boat sideways, straight in, grabbed him, wrangled him in the water,” he said.

The biggest concern was for the animal’s welfare, Collett said. “We’re about 2,500km away from freshwater crocodile habitat.”

The freshwater crocodile, Crocodylus johnstoni, is typically found in northern Queensland, the Northern Territory and Western Australia. “They’re native to the top end of Australia in the upper reaches of creeks, river systems and lagoons,” Collett said. He suggested the animal may have been an escaped pet.

The species is not naturally found in NSW and the Australian Reptile Park said it would not have survived the colder winter conditions.

The crocodile was transported to the reptile park, on the NSW Central Coast, and underwent health assessments by a veterinary team on Monday.

The crocodile was slightly shorter than a metre long, and the team believed it to be a subadult female. “Being a girl, it could be up to 10 years of age at that size,” Collett said. Large males of the species can reach up to 3 metres long, and females 1.5 metres.

NSW police said in a statement: “It is unknown how long the crocodile had been in the water or how it arrived there.”

Sightings of multiple reptiles had been reported by some Wallsend community members, but a spokesperson for NSW police confirmed “it was just the one crocodile” and there had been no further sightings reported since the capture.