Police in Christchurch cannot yet establish what substance led to six people being taken to hospital with breathing difficulties.
A jar containing a liquid was thrown through the bedroom window of a house on Pages Rd in the suburb of Bexley just before midnight on Christmas Eve.
Police say the occupants reported that the jar's contents had a bad smell, and when they arrived at the scene they found the two adults and four children having trouble breathing.
The officers themselves had to be decontaminated by the fire service, and their car was towed away for decontamination.
Detective Sergeant Sarah Illingworth says there appears no reason for the family to have been targeted but inquiries are continuing.