Police on Monday raided a rental house in the province of Samut Prakan, neighbouring Bangkok, and arrested 13 people, said Jirabhob Bhuridej, chief of the police's Central Investigation Bureau, at a press conference in the Thai capital.
Jirabhob said the Australian Federal Police (AFP) informed Thai authorities last year of a scam group led by an Australian and a British, and a joint investigation was launched.
The alleged scammers operated out of Thailand to swindle money from victims in Australia and potentially other English-speaking countries through online advertisements and phone calls to invest in long-term bonds with a promise of high returns, Jirabhob said.
Footage showed the men after being arrested in the rental house that was converted into an office.
Papers of alleged scam scripts and workflow were taped to their partitioned desks. There were also whiteboards the police said were used for tracking their progress, and clocks on a wall showing time zones across Australia.
Thai police said they staked out the house for several months and saw the men coming and going at times that coincided with working hours in Australia.
They said they confiscated a number of phones, computers and other electronic devices allegedly used for the scam.
AFP senior officer Kristie-Lee Cressy said at the Bangkok press conference that at least 14,000 Australians had fallen victim to this scam.
"The group amassed at least 1.9 million in (Australian dollars) from Australian victims in just the short time it had been operating. Money that we say was stolen from hard-working Australians and not invested as promised," she said.
"Shutting down this scam centre is a significant win for the communities of Thailand and Australia."
Australian authorities believe the two leaders of the group had been running scams for many years and operating in several countries, including Indonesia, where they had escaped arrest before being found in Thailand, Jirabhob said.
The group of men arrested in Thailand on Monday includes six British, five Australians, one Canadian and one South African, officials said.
They said the suspects denied all wrongdoing, saying that they believed they were working legally for a legitimate investment company.
Immigration officials said they entered Thailand with different kinds of visas, including for retirement and education.
Jirabhob said they were initially charged with racketeering and working in Thailand without a permit. He said further investigation could lead to more serious charges, including fraud and involvement in a transnational organised crime.
Australian police officer Cressy said Australia suffered an estimated damage of $A4.45 billion from online scams in the past four years.
A UN report in April said transnational organised crime groups in East and Southeast Asia are spreading their lucrative scam operations across the globe in response to increased crackdowns by authorities.
