Police in Greymouth say they expect the white powder which was in an envelope sent to a local man will be analysed on Monday afternoon.
The man took the envelope to police on Sunday after he discovered it contained powder and a sinister note.
The discovery led to police cordoning off a large part of the normally quiet Greymouth central business district for a couple of hours.
Testing of the powder had been held up due to the bad weather in Wellington, but is expected to occur early Monday afternoon.
The initial result is expected to be known fairly quickly, but if the powder shows traces of a toxic substance more testing may be required.