Suspicious white powder was flour

File photo / Martin Sykes

The unknown white substance found in an envelope posted to an Upper Hutt business was flour, according to Environment Science and Research.

Emergency services were called to a Lane St address in Wallacevillle after a staff member discovered the package.

The street was cordoned off after the powder's discovery and about 20 of the 40 staff at the business were decontaminated.

Senior Sergeant Dave Rose says testing by ESR scientists overnight has confirmed the white powder inside the envelope was flour.

Police are continuing their inquiries to identify who was responsible for the package.

- NZ Herald staff