Six people were found dead at an upmarket hotel in Bangkok on July 16, the Thai government said, as Prime Minister Srettha Thavisin ordered a swift investigation to stem any damage to the tourism sector.

Two of the dead were Americans of Vietnamese descent and four were Vietnamese nationals, according to Mr Srettha.

“From the preliminary examination of the scene, it was assumed that they had been poisoned,” said Major-General Theeradej Thumsuthee, chief investigator of the Metropolitan Police Bureau.

He added that there were signs that all six, before they died, drank coffee or tea. A preliminary autopsy did not find any injuries, he said. He also said a tour guide was being questioned.

Lieutenant-General Thiti Saengsawang, the Metropolitan Police commissioner, said in a news briefing that based on preliminary findings, “all of them were killed by other people”.

“We need to find out the motives,” Mr Thiti said. “What we can prove now is that they are not dead from suicide but from the killing of others.”

The food served to their room was left uneaten, while cups were empty and drinks appeared to be consumed, he said, according to Bangkok Post.

Only one victim had a facial wound, and police assumed the person fell onto a hard object, he said.

The Thai-language Matichon Online said police were now searching for two Vietnamese nationals who they said were deemed “persons of interest”.

The incident, which took place at Bangkok’s plush Grand Hyatt Erawan hotel, comes as Thailand looks to further promote its tourism sector, a key driver of South-east Asia’s second-largest economy.

“The Prime Minister has ordered all agencies to urgently take action to avoid impact on tourism,” the Thai government said in its statement.

A police official, speaking on condition of anonymity, dismissed earlier reports in the Thai media that the six people had been killed in a shooting.

“There is no sign of a shooting,” the official told Reuters.

The US State Department was “closely monitoring the situation and (we) stand ready to provide consular assistance,” a spokesperson said, referring questions on the circumstances of the deaths to local authorities.

The Vietnamese embassy in Bangkok did not respond to calls from Reuters.

Lumpini police were alerted to the incident at around 5.30pm.

Officers found three men and three women dead inside a room at the Grand Hyatt Erawan hotel.

All six were supposed to check out on July 16 and had their bags packed. 

The hotel has over 350 rooms and is located in a popular tourist district known for luxury shopping and restaurants.

More than 28 million foreign tourists visited Thailand in 2023, spending 1.2 trillion baht (S$44.8 billion) in the country, where other key sectors of the economy have been slow in recovering from the Covid-19 pandemic.

The government expects 35 million foreign arrivals in 2024, on the back of longer visa stay periods and waivers for several nationalities.

The tourism sector was shaken in October 2023 by a shooting spree at a luxury shopping mall, close to the Hyatt, in which two foreigners were killed, prompting government measures to improve confidence.

Asia News Network (ANN)/ REUTERS, AFP for Straits Times