A man was arrested at gunpoint after crossing police tape at the Ottawa war memorial as Prime Minister Stephen Harper laid flowers to commemorate the killing of a soldier.

Mr Harper and his wife were visiting the National War Memorial when police surrounded the man with their guns drawn and ordered him to the ground.

Ottawa Police said the man was arrested for "disturbing the crime scene", Reuters reported. It was not immediately clear what the man's intent was.

An officer at the scene said: "He crossed the tape. We told him not to. He didn't listen."

The moment was captured on camera and seen by a crowd, including members of the public and politicians, who had gathered at the war memorial.

In pictures: Ottawa shooting Show all 43 1 /43 In pictures: Ottawa shooting In pictures: Ottawa shooting Ottawa shooting Several police officers walk near downtown Ottawa In pictures: Ottawa shooting Ottawa shooting An Ottawa police officer runs with his weapon drawn outside Parliament Hill in Ottawa In pictures: Ottawa shooting Ottawa shooting A photograph of Corporal Cirillo just moments before the fatal shooting Twitter/Kamakazi19982 In pictures: Ottawa shooting Ottawa shooting Tourist Megan Underwood posed with Corporal Cirillo before the shooting Megan Underwood, via Facebook In pictures: Ottawa shooting Ottawa shooting Flowers placed at the gate of the John Weir Foote V.C. Armouries in Hamilton, Ontario where it is believed the soldier who was killed in the attack was based AFP In pictures: Ottawa shooting Ottawa shooting Police search cars and pedestrians as they leave the Alexandra Bridge near the Parliament Buildings in Ottawa AP In pictures: Ottawa shooting Ottawa shooting Armed police officers walk down Queen Street near Parliament Hill, close to the scene where the gunman was later shot and killed AP In pictures: Ottawa shooting Ottawa shooting Armed police teams enter Centre Block at Parliament Hill in Ottawa AP In pictures: Ottawa shooting Ottawa shooting A small plane equipped with surveillance equipment flies over the scene of multiple shootings in Ottawa AP In pictures: Ottawa shooting Ottawa shooting Head of RCMP Bob Paulson briefs Canadian prime Minister Stephen Harper on the shootings at Parliament Hill in Ottawa AP In pictures: Ottawa shooting Ottawa shooting An Ottawa police officer runs with his weapon drawn outside Parliament Hill in Ottawa AP In pictures: Ottawa shooting Ottawa shooting RCMP and Ottawa police cruisers on Wellington St. stand guard Getty Images In pictures: Ottawa shooting Ottawa shooting Properties in central Ottawa were forced to shut PA In pictures: Ottawa shooting Ottawa shooting An Ottawa police officer and service dog run up Metcalfe Street following shootings in downtown Ottawa Reuters In pictures: Ottawa shooting Ottawa shooting The Conservative Party caucus room is shown shortly after shooting began on Parliament Hill, in Ottawa In pictures: Ottawa shooting Ottawa shooting Police teams enter Centre Block at Parliament Hill in Ottawa AP In pictures: Ottawa shooting Ottawa shooting Police attempt to secure a portion of downtown Ottawa near Parliament Hill EPA In pictures: Ottawa shooting Ottawa shooting Armed RCMP officers approach Centre Block on Parliament Hilll EPA In pictures: Ottawa shooting Ottawa shooting Armed RCMP officers guard access to Parliament Hilll following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting Police officers take cover near Parliament Hilll following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting RCMP intervention team members clear the area at the entrance of Parliament hill in Ottawa In pictures: Ottawa shooting Ottawa shooting Armed RCMP officers race across a street on Parliament Hilll following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting A still image captured from video footage by the Globe and Mail newspaper shows police officers responding to shooting attacks inside the Centre Block of the Parliament buildings in Ottawa Reuters In pictures: Ottawa shooting Ottawa shooting A police officer holds back the public from Canada's National War Memorial as CPR is performed on a shooting victim in Ottawa In pictures: Ottawa shooting Ottawa shooting Paramedics and police pull a victim away from the Canadian War Memorial in Ottawa In pictures: Ottawa shooting Ottawa shooting Emergency personnel tend to a soldier shot at the National Memorial near Parliament Hill in Ottawa. The soldier was standing guard when an unknown gunman shot him In pictures: Ottawa shooting Ottawa shooting Police and medical personnel moving a wounded person into an ambulance at the scene of a shooting at the National War Memorial in Ottawa In pictures: Ottawa shooting Ottawa shooting A police officer closes off the scene near the Canada War Memorial following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting Armed RCMP officers guard the front of Langevin Block on Parliament Hilll following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting A car thought to be the car of one of the suspects is pictured on Parliament Hilll following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting Police officers guard Parliament Hilll following a shooting incident in Ottawa In pictures: Ottawa shooting Ottawa shooting A Royal Canadian Mounted Police intervention team walks past a gate on Parliament hill in Ottawa In pictures: Ottawa shooting Ottawa shooting A heavily armed Royal Canadian Mounted Police officer stands guard at 24 Sussex, the residence of Canada's Prime Minister Stephen Harper after a reported shooting at Parliament building in Ottawa In pictures: Ottawa shooting Ottawa shooting A police officer secures the scene of a shooting on Parliament Hill in Ottawa In pictures: Ottawa shooting Ottawa shooting A Royal Canadian Mounted Police intervention team responds to a reported shooting at Parliament building in Ottawa In pictures: Ottawa shooting Ottawa shooting Police at the scene of a shooting at the National War Memorial in Ottawa In pictures: Ottawa shooting Ottawa shooting A heavily armed RCMP officer enters 24 Sussex Dr., the official residence of the Prime Minister In pictures: Ottawa shooting Ottawa shooting Quebec Premier Philippe Couillard makes a statement in regarding the shooting at the Parliament in Ottawa at the legislature in Quebec City. A soldier standing guard at the National War Memorial in Ottawa has been shot by an unknown gunman and there have been reports of gunfire inside the halls of Parliament In pictures: Ottawa shooting Ottawa shooting Police cordon off a street leading to Parliament Hill in Ottawa In pictures: Ottawa shooting Ottawa shooting Police vehicles block a road near Parliament in Ottawa In pictures: Ottawa shooting Ottawa shooting An ambulance arriving at the scene Eric Twitty In pictures: Ottawa shooting Ottawa shooting Emergency vehicles at the National War Memorial following a shooting incident in Ottawa Gerry Byrne In pictures: Ottawa shooting Ottawa shooting Canadian police outside Parliament Mike Kujawski

Corporal Nathan Cirillo was killed after a gunman opened fire at the National War Memorial just before 10am on Wednesday.

The gunman is believed to have then driven in a car up to the Parliament Centre Block, where a gun fight with police took place before he was shot dead by sergeant-at-arms Kevin Vickers.

The House of Commons was set to open on schedule at 10am on Thursday, with the prime minister due to speak at that time.

Tighter security was evident all over the sprawling parliamentary zone in downtown Ottawa.

Meanwhile, the flag flying over Parliament's Centre Block, where the gunman had burst in on Wednesday morning, was at half mast.