The four French tourists filed complaints with police after the attack on the island of Koh Kut, a popular destination for European backpackers off Trat province, 280 kilometres south-east of Bangkok, a Trat police official told dpa.
Three of the victims were in serious condition at Koh Kut Hospital, at least one of them with a knife wound, news reports said.
Three of the suspects were apprehended late Saturday, after a manhunt by around 50 soldiers and marine police, villagers and staff from the tourists' hotel.
The other two were arrested Sunday night as they tried to cross the border into Cambodia, according to local media reports.
National Police Chief General Chakthip Chaijinda was en route to KohKut Monday to personally question the suspects, Thai news media reported.
Thai authorities came under intense international criticism for their investigation of the 2014 murder of a British man and woman on another beach resort, and the sentencing of two migrant workers from Myanmar to death.
- DPA