BUENOS AIRES, Argentina -- A whale appeared in the marina of one of Buenos Aires' most exclusive neighbourhoods Monday, periodically surfacing alongside luxury yachts while hundreds of onlookers tried to capture the moment with smartphones.

The whale first surfaced in the early afternoon in Puerto Madero, an upscale area of towering office buildings and high-end lofts. In the middle of the area is a body of water the size of a few square blocks where many residents keep boats.

News of the whale quickly spread on social media and was broadcast live by local stations, prompting hundreds to line up along the port area to catch a glimpse.

"We were at home having lunch when we saw it on the news and said, 'We have to see this for ourselves,"' said Rosana Saavedra, a teacher who came with her husband and teenage daughter. "We were so curious. What is this whale doing here?"

Puerto Madero was built in the late 19th century to better accommodate an increasing number of ships coming into Buenos Aires, one of South America's largest port cities. After decades of decay, it was transformed by a major urbanization project in the 1990s and today is one of the city's trendiest districts.

Authorities had not identified the type of whale, and it was unclear how they would get it back to the ocean. A port police boat was seen going up and down the waterway, apparently trying to lure the animal to the connecting Rio de la Plata river, which feeds into the Atlantic.

Police at the scene declined to answer questions. Calls to the Puerto Madero police headquarters were not answered.

Within a few hours, the normally sedate quarter with pricey coffee and pastry shops had a carnival feel as vendors sold cotton candy and soda and families with small children kept an eye out for the whale.

Each time the whale surfaced, people in the crowd gawked and rapid-fire clicks of cameras pierced the air.

Many Argentines, known for their quick wit and humour, were ready with jokes.

Irene Fernandez, who owns a condo a block from the water, said she was surprised by the crowd when she came out for her afternoon walk. She asked a police officer what was happening and was told a whale had appeared.

"I always see whales walking around here," she said, making a play on the word "ballena" in Spanish, which Argentines sometimes use to refer to politicians and people who are portly.

Still, there was also worry about what might happen to the creature.

"It's really said," said Daniela Ritta, who works at a bank around the corner from the marina and went with colleagues to have a look. "This is not its natural habitat. The poor whale is clearly lost."

Mariano Sironi, scientific director of the Whale Conservation Institute in Argentina, initially said the animal appeared to be a minke or a humpback whale. But later, after viewing video and talking with a colleague, he said he thinks it is a humpback.

Sironi said whales sometimes get disoriented and swim upstream in rivers. When that happens, the animal often needs help to get back to sea, which usually involves using boats to direct it back from the direction it came.

A fresh-water environment like a marina can hurt the skin of whales, provides no food and also makes it harder for them to swim because the water doesn't have the buoyancy effect of salt in the ocean, Sironi said.

While there is no time limit on how long a whale can live in fresh water, "every day it will get weaker and be in worse health," he said.