A C-130 cargo plane from Brazil's air force has flown almost 400 stranded penguins to a southern beach so the animals could swim back home in Argentinian and Chilean waters.

Volunteers from the International Fund for Animal Welfare (IFAW) set the Magellanic penguins free off the coast of southern state of Rio Grande do Sul, near the Uruguayan border, on Saturday.

The birds were part of the 1,000 penguins that strayed into Brazil's northeastern beaches in recent months while on their seasonal migration to the country's southwest. Many that were not fit to travel were left at IFAW's animal facility in the northeastern city of Salvador while 20 percent of the number died.