An extreme drought in parts of the Amazon has led to a dramatic drop in river water levels, exposing dozens of usually submerged rock formations with carvings of human forms that may date back some 2,000 years.

Livia Ribeiro, a longtime resident of the Amazon's largest city, Manaus, said she heard about the rock engravings from friends and wanted to check them out.

"I thought it was a lie ... I had never seen this. I've lived in Manaus for 27 years," said Ribeiro, an administrator, after viewing the dazzling relics.

The rock carvings are not usually visible because they are covered by the waters of the Negro River, whose flow recorded its lowest level in 121 years last week.