Dutch prosecutors say they have launched co-ordinated raids in several countries against suspected money-launderers and tax evaders.
They are investigating about 3,800 Dutch-linked accounts in an unnamed Swiss bank following a tip-off they could contain undeclared assets.
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 more than 50,000 suspect accounts at the bank.
Meanwhile, UK authorities said the investigation was also targeting senior bank employees.