Police said they were called at 9:52am local time on Wednesday with a report of shots fired at the memorial. Paramedics said they attended to a uniformed soldier before he was taken to hospital.
The gunman then moved to nearby Parliament Hill. Video obtained by Canada’s Globe and Mail showed police moving through the parliament buildings before multiple shots were heard in an apparent exchange of gunfire.
A Globe reporter inside parliament told Al Jazeera that a body was seen on the ground after the gunfire, although the identity of the casualty was not confirmed.
One witness, Marc-Andre Viau, told the AFP news agency that he saw a man run into a meeting inside parliament, chased by police who yelled “take cover”. That was followed by up to 20 gunshots.
Speaking to Al Jazeera from inside parliament at 11.30am local time (15.30 GMT), Senator Jim Munson said: “The building is in complete lockdown. People are quite shaken. This kind of terrorist attack did not seem possible. It is my understanding that one shooter has been killed and there could possibly be three.”
Those details have not been confirmed by police, but they have said they were searching for one or more people and investigating several reports of gunfire – at the memorial, Parliament Hill and near the Rideau Centre, a shopping centre.
“Shots fired inside centre block during our caucus meeting. I’m safe locked in a office awaiting security.” Kyle Seeback, an MP, said on Twitter
The gunman was described as heavy set, carrying a long weapon and disguising his face with a scarf.
People fled parliament by scrambling down scaffolding being used in renovations, witnesses told the Canadian Press news agency.
The spokesman for the prime minister, Stephen Harper, said Harper was safe and had left Parliament Hill.
Canada raised its terrorism threat level from low to medium hours before the attack, the highest it has been for four years.
The incident comes two days after two Canadian soldiers were run over – and one of them killed – in Quebec.