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The white substance found in an envelope posted to an Upper Hutt business is not toxic, police say.

Emergency services were called to 32 Lane Street, Wallaceville, this morning after a staff member discovered an envelope containing a white powder about 9.15am.

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

However, police this afternoon said preliminary results by the Environment Science and Research (ESR) indicate the powder is not toxic. Further testing by ESR will be conducted overnight to confirm the exact nature of the substance.

Staff have now been allowed to re-enter the building, which is home to Hewlett Packard Enterprise Services.

Employee Danny Poulson posted on twitter soon after the callout that he had "just got evacuated from work, and detained briefly while emergency services checked things out, Lane St is currently cordoned off".

Police will continue to investigate who was behind the incident.