They said the Armed Offenders Squad has been deployed as a precaution, but will not give any further details.
Earlier, a 46-year-old man was charged following the death of teenager Connor Whitehead of Northcote.
Police charged the man last night with being an accessory after the fact to murder and he is due to appear in the Christchurch District Court tomorrow.
Police are confident they know who was involved in Connor’s death and say the arrested man assisted the people directly involved.
Police hope the man’s arrest will “serve as a warning to anyone who may be assisting those involved”.
They are providing Connor’s whānau with support alongside Victim Support.
Connor is the second 16-year-old to die at a gathering in the city in three months.
Zion Purukamu of Hoon Hay was fatally stabbed at a party in Fendalton on 13 August.
Officers are continuing their inquiries into Connor’s death, and want to speak to anyone who was in the area at the time.
They can be contacted on phone number 105 and event number P048523046 should be quoted.
Information can also be provided anonymously via Crime Stoppers on 0800 555 111.
A Give a Little page has been set up to raise money for Connor’s mother and two siblings.