Adelson Cerqueira Silva, of the federal environmental agency, said about 300 penguins have been found dead or alive in recent days along the coast of Bahia state, better known for sunbathers in bikinis than for seabirds native to Antarctica and Patagonia.

The state capital, Salvador, is roughly 600 miles closer to the equator than Miami is and temperatures in the current Southern Hemisphere winter are in the mid-70s (low 20s centigrade).

"This is unheard of. There have even been reports of penguins washing up as far as Aracaju," Mr Silva said, referring to a beachside state capital even closer to the equator.

He said biologists believe stronger-than-usual ocean currents have pulled the birds north. Others have suggested the increase might be due to overfishing near Patagonia and Antarctica which has forced the penguins to swim further in search of food.

Mr Silva said the environmental authority was receiving hundreds of phone calls reporting penguin sightings.

"We're telling people if the penguins don't appear to be injured or sick to leave them alone so they can swim back," he said.

While penguins commonly wash up as far north as Rio de Janeiro state in July and August - hundreds have done so this year - Bahia is roughly 750 miles north-east of Rio.

P Dee Boersma, a conservation biologist at the University of Washington who works with penguins in Argentina, said that while she has heard of penguins occasionally washing up as far north as Bahia, the numbers washing up this year are extremely high.

"The last time that you got a lot of penguins was in 2000, mostly in Rio but some further north. That year the sea surface temperature was a degree lower than the 30-year average so the penguins just keep swimming in search of food without noticing where they're going," she said.