Four Thai officials have been dismissed after authorities found more than two billion baht ($57 million) in their bank accounts, with investigators calling the group "unusually wealthy".

Corruption is rife in the Southeast Asian kingdom, with officials often accused of accepting small bribes and pay-offs, but sums of this magnitude are rare.

The approximately $57 million was discovered in multiple accounts held by three women and a man who work in the Revenue Department in Samut Prakhan province near the capital Bangkok.

The National Anti-Corruption Commission has referred the case to the attorney-general's office and requested that the Criminal Court for Corruption also investigate.

The four were "unusually wealthy", said Sornchai Chuwichian, assistant secretary-general and deputy spokesperson of the NACC.

Their listed assets — including their bank deposits — did not match their government incomes, Sornchai said in an NACC statement Monday.

None could explain the source of the money, Sornchai said.

The man, Danai Damrongchaiyothin, had 1.1 billion baht ($31 million) in seven accounts, while one of the women held more than 500 million baht ($14 million) in five accounts.

A starting salary for a revenue official is less than $450 per month.

All four have been dismissed from their government posts, according to the NACC statement. It did not mention whether they had been charged or arrested.