An enormous fire is destroying vast stretches of the Amazon rainforest in Peru, threatening natives and wildlife, officials said, blaming traditional slash-and-burn farming.

The fire broke out on September 10 in an indigenous community called Pitsiquia, in the heart of the Peruvian Amazon, said the National Civil Defense Institute.

It has since destroyed more than 19,000 hectares (47,000 acres) of forest -- an area more than three times the size of Manhattan -- and another 200 hectares of farmland in the Junin region, said the disaster response agency.

"We still have not managed to bring it under control," it said in a statement.

Air pollution caused by smoke is causing eye problems for inhabitants, said local health authorities.

The fire is in an extremely remote region known as VRAEM, an acronym for the Apurimac, Ene and Mantaro river valleys.

The area is known for its isolation, dense rainforest and tropical crops -- coffee, cocoa and the country's largest tracts of coca, the raw ingredient for cocaine.

Authorities are worried the fire could wreak chaos on a major indigenous reserve, home to native communities that have limited contact with the outside world, and spread to the Otishi National Park nearby.

"The focus of the fire, the most dangerous part, has entered the Ashaninka reserve. It's advancing very quickly," said Jimmy Laura, a spokesman for the Rio Tambo municipal district.

"If the fire crosses the reserve, it will reach the national park," he told AFP.

The reserve is home to some 5,000 people in 10 communities.

Officials said a drought had left the region vulnerable. The fire then broke out when local farmers were burning a pasture to clear it for planting.

"Unfortunately, this practice can get out of control," said Marco Pastor, an adviser at the national parks service.

He said a newly launched Peruvian satellite, PeruSAT-1, was being used to monitor the fire and assess the damage.