Trade surplus for the month reached 3.3 billion francs (€2.6 billion, $3.9 billion), boosted by three more working days in May than a year ago.
When stripped of this positive effect, trade surplus "stagnated as imports – Vietnam effect –collapsed."
Vietnam has been sending billions worth of gold ornaments to Switzerland, a key gold smelting country, over recent years to be melted down into bars.
In May however, Switzerland noted that the "disappearance of the gold ornaments imported from Vietnam" shaved 918 million francs off imports.
According to Vietnamese media, authorities are working on a decree which proposes to tighten restrictions on gold trading, including for export.