A British backpacker has been discovered dead on the popular Thai tourist island of Koh Tao, police say, four months after a British couple were found murdered there.

Police said the body of Christina Annesley, 23, was discovered inside a bungalow room at a resort on the eastern side of the island on Wednesday.

There were no immediate signs of criminal activity but her body will be sent to the mainland for an autopsy.

"There was no trace of a fight and her body has no wounds," local police officer Lieutenant Colonel Napa Senathit said by telephone, adding that investigators discovered three kinds of medicine in her room, but no recreational drugs.

The autopsy is not likely to be carried out before Sunday as officials have to wait for a ferry to the mainland.

"There is no ferry today so we will send her body on Saturday night to arrive on the mainland Sunday morning," Lieutenant Colonel Napa said.

British daily The Telegraph said Christina's mother Margaret had posted on her daughter's Facebook page saying she had died of "natural causes".

The Facebook page appeared to be inaccessible on Friday.

"We have lost our beautiful daughter Chrissie in Thailand of natural causes," the paper reported her writing.

"We are totally devastated. We love you so much darling, rest in peace. We will bring you home soon xxxxxxxxxx Mum and Dad."

Last year Koh Tao, a small island of white sand beaches and azure waters in the Gulf of Thailand, was rocked by the double murder of two young British backpackers - David Miller, 24, and Hannah Witheridge, 23.