Thai police are investigating the suspected murder of a Swiss woman whose body was found near a waterfall at a popular beach resort.

Police found the woman, named Nicole Sauvain-Weisskopf, lying face down covered in a black sheet, in the water among rocks on Phuket island on Thursday.

The case casts a shadow over Phuket's so-called "Sandbox" scheme, a pilot project to reopen Thailand's Covid-devastated tourism sector after more than a year of draconian travel curbs.

The 57-year-old victim had travelled to Phuket under the scheme, which allows vaccinated travellers to visit the island without going through Thailand's otherwise mandatory two-week hotel quarantine.

The cause of death has not been revealed but national police chief Suwat Jangyodsuk said there were signs of violence on the body and officers believe Sauvain-Weisskopf was murdered.

Phuket's 'Sandbox' scheme allows vaccinated travellers to visit the island without going through quarantine
Phuket's 'Sandbox' scheme allows vaccinated travellers to visit the island without going through quarantine AFP / Lillian SUWANRUMPHA

Officers found the woman's phone, shorts and trainers near the body.

Phuket governor Narong Woonciew pledged to "do everything to investigate what happened and bring justice to Ms Nicole".

Andrea Kotas Tammathin, honorary Swiss consul in Phuket, lamented what she called "a sad, sad day for the Phuket community".

More than 16,000 people have arrived in Phuket since the July 1 launch of the Sandbox scheme.

Prime Minister Prayut Chan-O-Cha has expressed his condolences to the victim's family and asked to be regularly updated on the probe, a government spokesman said.