Leopard seals breed in Antarctica, where they are most commonly found, but small numbers regularly visited southern and central New Zealand during winter each year.
"It is unusual to see them around Auckland," Mr Duffy said.He said people should avoid leopard seals because they were dangerous, and had been known to act aggressively towards divers in Antarctica.
"Although the animal at Kohi is a juvenile, people should still keep their distance from it and avoid swimming or kayaking near it."
Leopard seals are the most predatory of the seals, with a diet that consisted predominantly of penguins and other seals.
DoC spokesman Nick Hirst said the fact seals were re-colonising New Zealand's beaches was an encouraging sign for the health of the country's coastline.
"New Zealand seals are a natural part of our coastal environment."However, people needed to remember seals were wild animals, and it was best to watch from a safe distance of about 20m, he said.
The two furry invaders that came ashore today appeared to arrive for entirely different purposes.
The leopard seal was spotted on Kohimarama Beach having a lazy day in the sand, while the other had ventured all the way to Middlemore Hospital.
Amanda Provan, 22, who works in Kohimarama, said a customer came in and told her about the seal.
When Ms Provan first saw the seal at 9.30am, there was a crowd of about eight people, she said.
"It is still there now, and the crowd has just been getting bigger and bigger.
"It's the first time I have ever seen a seal on Kohimarama Beach, which is very exciting. I think it's also quite unusual to see a leopard seal in Auckland."
The seal looked happy and healthy, she said.
"It was getting some sun rays and just having a good sunbathe."
The fur seal was waiting outside Middlemore Hospital as the early morning shift was about to start.
Counties Manukau District Health Board spokesperson Lauren Young said she estimated the seal may have got there via the estuary at the back of King's College.
"He was getting a bit grumpy, perhaps because he might have been waiting there about six hours for admission," she said.
The Department of Conservation arrived about 8am this morning and returned the seal to the sea, she said.
Seals in New Zealand:
• The last leopard seal to visit the Auckland area was in Glendowie in 2013, and before that in Herne Bay in 2011.
• It is estimated there are between 100,000 and 200,000 fur seals in New Zealand in comparison with the estimated 2 million living here in the early 1800s. A law to protect seals was passed in 1875 after numbers dwindled due to sealing.
• Non-breeding colonies of New Zealand fur seals are found around Oaia Island and the Poor Knights Islands..
Advice from DoC
• Always stay at least 20 metres away.
• Never attempt to touch or handle seals as they can be aggressive if threatened.
• Seals carry diseases that can be passed to humans and people have diseases that can make seals sick.
• Seals can and do bite, and they can move very quickly.
- Ensure you keep small children at a safe distance, and always keep dogs on a leash, under control and away from seals.
- Do not disturb seals. Don't make loud noises or throw things at them.
- Do not feed seals, as it encourages them to approach people in the future.
- Call DoC on 0800 362 468 if a seal is severely injured, entangled in a net or rope, in danger from dogs, traffic or other human activity.
