Emergency services are investigating a mysterious white powder which was sent in a letter to Wellington's spy headquarters.

A New Zealand Intelligence Community spokesperson confirmed the powder had been sent to Pipitea House in central Wellington.

The building is home to the Government Communications Security Bureau (GSCB) and the New Zealand Security Intelligence Service (SIS).

"Emergency services are attending as part of a standard response procedure," the spokesman said.

"The Intelligence and security agencies take incidents like this seriously to ensure the safety of our staff."

A spokeswoman for Fire and Emergency New Zealand said there was limited information but they were investigating the substance.

She said it was found at an address on Pipitea St in central Wellington around 3pm.

Police have been approached for comment.