Dutch prosecutors say they have launched co-ordinated raids in several countries against suspected money-launderers and tax evaders.
They said they had been tipped off about millions of dollars of undeclared assets linked to 3,800 Dutch-linked accounts in an unnamed Swiss bank.
Paintings, a gold bar, cash, a luxury car and jewellery have been seized.
As well as the Netherlands, there have been searches in France, Germany, the UK and Australia.
The Dutch government has passed information to the other countries about 55,000 suspect accounts at the bank, Reuters news agency reported.
The co-ordinated raids began on Thursday, the Dutch office for financial crimes prosecution (FIOD) said in a statement.
The Netherlands raids targeted homes in four locations – The Hague, Hoofddorp, Zwolle and the municipality of Venlo. Two people were detained for interrogation.
The investigation will continue for weeks to come, financial prosecutors said.