The bloodied body of a 27-year-old German woman was found on Sunday buried under dried leaves and rocks on the picturesque island of Koh Sichang in the Gulf of Thailand.

She was "badly beaten" on her face and skull, police spokesman Krissana Pattanacharoen said in a statement.

The suspect was identified as 23-year-old Ronnakorn Romruen.

Police say he encountered the German tourist, who entered the country on March 23, near the crime scene and raped her.

"The suspect feared that she would notify the police so he used a rock to hit her on the temple and face," Krissana said.

He was arrested a few hours later in his home, wearing a blood-stained shirt and pants, police say.

Authorities charged him with premeditated murder, rape and concealment of a body, said Sichang police superintendent Atthakoon Salakoon.

"He confessed to all the charges and admitted he took drugs before committing the crime," Atthakoon told AFP.

Thailand is expected to receive upwards of 40 million tourists this year.

While the Southeast Asian country is generally considered safe among travellers, several high-profile incidents have tarnished its reputation in recent years.

In 2014, the battered bodies of two British backpackers were found on a beach in Koh Tao.

Two Myanmar migrant workers were sentenced to death for the murders after a controversial investigation and trial that were criticised by observers.

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