A gunman shot and killed a soldier at a war memorial in Ottawa, then ran into the parliament building where he exchanged gunfire with police.
One gunman is dead, but parts of Canada’s capital remain on lockdown as police hunt for more suspects.
At a press conference, police said the situation was “ongoing” and “fluid”.
It came hours after Canada raised its terror threat level, after another soldier was killed on Monday in a hit-and-run attack by a Muslim convert.
The country earlier this month announced plans to join the US-led campaign of air strikes against Islamic State (IS) militants in Iraq.
But there is no confirmation any of this week’s attacks are linked to IS or the new military campaign.
The latest incident began when soldiers guarding the memorial came under fire on Wednesday morning.
One gunman – said to be carrying a rifle – fired on soldiers guarding Canada’s main war memorial and then ran into the parliament.
“Shots fired at War Memorial at 9:52am today; one person injured,” Ottawa Police tweeted.
A statement by Ottawa Police confirmed the soldier had died from his injuries.
Dozens of shots were fired inside the parliament building, Canadian MP Marc Garneau told the BBC.