"Police have begun a scene examination and expect to be there for some time," he said.
Armstrong told reporters it was "far too soon" to give any further details on the incident, including what injuries the woman sustained.
One local resident, Janelle Hague, said it was "a bit frightening" to see this happen in a "good area".
"We don't want this in our neighborhood because of our kids."
She described hearing a large bang this morning that sounded like "fireworks".
Police, fire and ambulance teams are at the scene.
May Road is blocked off by two police cars at the Dominion Road intersection and traffic is being directed away from the scene.
Fire engines are blocking any view of the scene, which appears to be at a residential property near a side street.
Confused residents within the cordon are out on the street, or peeking out of their curtain windows.
There are numerous police officers, along with fire and emergency staff.
St John were called to the incident at 7.37 this morning and sent three units, a St John spokeswoman said.
This included one ambulance crew, a rapid response unit and one manager.
May Rd is closed between Stoddard Rd and Memorial Ave, Auckland Transport says.
More details to follow.
