UPDATED 11.19am: New Zealand's terror threat level could be raised, as a result of the siege at Canada's Parliament.

And John Key's expecting some will say the shooting is payback for Canada joining the fight against ISIS.

In media "talking points", accidentally sent to Newstalk ZB this morning, MFAT has advised Mr Key to call the shooting a "terrible act of violence" - and to say the motivations for it should become clearer in the coming days.

The Prime Minister will tell media he expects there to be debate on whether the shooting is retaliation for Canada's role in the anti-IS fight - but it's "important to let the facts emerge from this incident".

He says our government is still considering options for a role in that battle.

And while the terror threat here was recently lifted from "very low" to "low", it's under constant review.

Key offers condolences to killed Canadian guard

Prime Minister John Key has expressed his deepest sympathies to those affected by today's shootings in Ottawa, naming it a 'senseless act of violence'.

He says he will be personally extending New Zealand's sincere condolences to Prime Minister Stephen Harper and the people of Canada.

Mr Key says our two countries have a long standing warm and close relationship, and today we stand beside them in solidarity.