The number of elephants that died trying to save a baby elephant from drowning in a national park in Thailand has risen to 11, officials say.

Thai authorities on Saturday initially said six elephants had died after a roughly three-year-old elephant drowned at Khao Yai National Park, about 135 kilometres north-east of Bangkok.

Two live elephants stuck on the edge of the Haew Narok waterfall. Credit:Department of National Parks

Five other elephants were thought to have jumped into Haew Narok Waterfall to try to save the baby.

A drone has since located another five dead elephants near Haew Narok, the park's highest waterfall, the Associated Press reported.