More than 300 whales have been found washed up in a remote inlet in Patagonia in southern Chile in one of the largest die-offs on record.
"It was an apocalyptic sight. I'd never seen anything like it," said one of the scientists who made the discovery, Vreni Haussermann of the Huinay Scientific Centre.
Scientists launched an expedition to count the animals after 20 sei whales were reported dead in April, beached in an extremely remote region some 2000km south of the capital Santiago.
When the researchers flew over the region in June, they found the scale of the die-off was much larger: at least 337 dead whales, "including bodies and skeletons," said Haussermann.
"There are still a lot of areas we haven't managed to reach, so it's likely there are more dead whales," she told AFP.
The die-off, the biggest single event of its kind known to science, will be investigated in an upcoming issue of National Geographic magazine, which funded the expedition.
Scientists initially said the whales did not bear any wounds, suggesting they may have died of a virus or a harmful algal bloom known as "red tide."
The gruesome find comes as countries get down to tough negotiations at crunch talks in Paris, which are seeking a pact to curb climate change.
Marine biologists say the warming of the world's oceans is putting dangerous pressure on whale populations by killing off their food supply and changing their age-old migratory routes.