Yesterday, he was not backing away from that warning and while he refused to give details, he responded to those who had suggested he was scaremongering by saying: "If anyone believes there is absolutely no risk of a form of domestic terrorism here then they're actually deluded."
The most immediate manifestation of the terror threat was the rapid rise of Islamic State (Isis).
About 3000 Isis fighters in Iraq and Syria had Western passports, including a small number of Kiwis.
"They threaten to return to their countries of origin both radicalised and with military training."
Mr Key said he was also aware of several Kiwis seeking to travel overseas to fight for groups such as Isis and that the group was running a sophisticated social media campaign to identify and recruit NZ jihadists.
New Zealand's intelligence and security framework was to be reviewed next year, but "the issue of foreign fighters is an immediate and rapidly evolving one that cannot wait to be considered as part of that wider review", the Prime Minister said.
The immediate review was due to take four weeks and Mr Key expected it would recommend law changes which he hoped to pass under urgency before Christmas. He would seek Opposition support, and yesterday offered to brief leaders of other parties on the underlying issues.