Volcanic ash raining down from the Chilean volcano Chaiten may cause long-term environmental damage and harm the health of people and animals in Patagonia, scientists say.

Ash from the volcano, which started erupting 10 days ago for the first time in thousands of years, is made up of pulverised rock containing all kinds of minerals.

It has spoiled lakes, rivers and lagoons, coated plants in a dense layer of gray, and altered the sensitive habitat of animals now struggling to survive. Satellite images show a white stripe smeared across the southern part of South America.

Though it is too early to say what the long-term effects will be, ecologists say life has permanently changed in the region's pine and cypress forests, inhabited by pumas and huemules, a rare species of deer.

"I am tremendously worried because this is an environmental, social and ecological disaster," said Alejandro Beletzky, an environmental scientist in a soot-covered swath of Argentina.