MSD regional commissioner Dianne McDermott said "the safety of our clients and staff remains our top priority".
"As this is now a police matter, we're unable to comment further."
A police spokeswoman said officers were called to an address on Aldwins Ave about 8.50am in response to a report of a threat.
"Early indications are it may be mental health related, however, police are on scene now and we are waiting to hear back from local staff," said a spokeswoman.
"One person is speaking with police in relation to the incident."
The doors to the office reopened about 10.35am.
NZME reporter Tim Cronshaw was at the scene - he said the doors were locked and no one was allowed in or out of the building as MSD customers queued outside.
Cronshaw said a man was taken into police custody and escorted out of the building by officers.
