Another five elephant carcasses have been discovered downstream from a waterfall where the bodies of six others were found on the weekend.
The heightened death toll makes this the incident with the most elephant casualties at Khao Yai, where eight elephants fell to their deaths at the same waterfall in 1992, the AP reported.
There are around 300 wild elephants in the park, which is home to various wild animals, including bears and gibbons, and is a popular destination for tourists.
The carcasses were discovered after the first six elephants plunged to their deaths at the Haew Narok - "Ravine of Hell" - waterfall in Khao Yai National Park in northeastern Thailand, said Sompote Maneerat, spokesman for the National Parks, Wildlife and Plant Conservation Department.
The elephants were trying to cross the river at the top of the cliff when a strong current swept them over the edge of the waterfalls, officials at the Department of National Parks, Wildlife and Plant Conservation said.
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The additional five were spotted by drone near a risky waterfall commonly known as, 'Hell's Fall'. The young elephant did not survive and officials later found five other drowned elephants on the first level of the large three-tiered waterfall, which has been temporarily closed to visitors.
Rangers managed to lead the two surviving elephants, who were trying to reach the calf, from the ravine and said they will monitor their condition throughout the week.
Two other elephants who were stuck on a ledge and extremely distressed were rescued.
Nearly an entire herd fell into the waterfall in Khao Yai National Park. Efforts are also underway to prevent similar incidents from happening.