Thailand’s Matichon newspaper and other Thai media initially reported a shooting in the country’s capital on Tuesday evening, citing local police.
However Matichon later said the cause of death had been established as poisoning.
The attack was reported to have taken place at the five-star Grand Hyatt Erawan. Pictures have emerged of police entering the lobby of the hotel.
Thailand's Foreign Ministry said in a short statement that the dead were reported to be two Vietnamese Americans and four Vietnamese nationals.
It said three of the dead were men and three were women.
A police official, speaking on condition of anonymity, dismissed earlier reports in Thai media that the six people had been killed in a shooting.
"There is no sign of a shooting," the official told Reuters, without elaborating further.
Thailand’s prime minister has ordered an investigation into the incident.
Medical services could not immediately be reached for comment.
Matichon initially said reports had emerged of a shooting at a “luxury hotel” in the Ratchaprasong district of the city at 7.30pm local time (1.30BST).
It said five people died inside a room and one person outside.
The Grand Hyatt Erawan is described on its website as a five star hotel in the capital’s key commercial and diplomatic district, next to Erawan Shrine. It has 380 rooms and 44 suites and its luxury facilities include a spa and restaurant.
Ratchaprasong is a shopping and entertainment district next to the well-known Siam area, which is dominated by large shopping malls such as MBK Center.
MICHAEL HOWIE
