© James SmithThe penguin is in a healthy condition, experts say.
The closest king penguin colony is on Macquarie Island, about 1,500 kilometres south of Hobart.
Marine Conservation Program wildlife officer Dr Julie McInnes said the sighting at Seven Mile Beach was exciting.
"It's a pretty rare thing to see king penguins up here in Tasmania, it's quite a way north from the usual range," Dr McInnes said.
"It's not unheard of, we have seen them a couple of times in different parts of the state."
Dr McInnes said it was not clear if the bird was lost — it may have come ashore to rest after a big fishing trip, or was undergoing its annual moult.
Penguin 'fat and healthy'
Dr McInnes said penguins underwent what is known as a 'catastrophic moult', where they come ashore to lose all their feathers over a few weeks.
"They tend not to go back into the water during that time because their feathers are no longer waterproof," she said.
If it was resting after a big fishing trip, it may be gone from the area within a few days, she said.
Dr McInnes said the penguin was in good condition and did not appear to be injured.
"It looks like quite a fat penguin which is always nice," Dr McInnes said.
She said outside the breeding season penguins would swim well away from colonies in search of food, and did not need to moult at their home base.
King penguins are the second largest penguin species.
Tremendously beautiful!!