Residents were evacuated from the Sheffield Cres area in Burnside about 2.20pm and a police cordon was erected around the scene.
The area was cordoned off for about three hours while police, firefighters and Defence Force staff dealt with the "explosive substance".
A staff member at a business in the street told The Press the owner of a warehouse told him he found picric acid while clearing it out on Thursday.
"He found some old picric acid stored there for years and years and he didn’t know what to do with it," the man told The Press.
"He was so casual about it. I don’t think he was expecting what happened."
Picric acid (-trinitrophenol) is a bright yellow organic substance that is highly explosive and sensitive to shock, friction, and heat.
It is used in laboratories for staining and as an explosive and dye.
The staff member told The Press a pile of sand was used to cover the acid.
Senior Sergeant Craig Ellison warned the public to avoid the area on Thursday afternoon.
Some businesses were evacuated, including Orion and a dance studio on Sheffield Cres.
Kate Limuloa, of Silhouette Studios, told RNZ yesterday she left just after 3pm. But she said none of her 15 dance students received the alert.
A nearby gym told RNZ only one client received the emergency alert.
-Allied Media with RNZ
