A man was arrested a few metres away from Stephen Harper Wednesday, as the prime minister prepared to lay a wreath where a soldier was shot and killed the day before.

Ottawa police arrested the man after he crossed the yellow police tape blocking off the National War Memorial.

It's unclear why the man crossed the police lines, but officers said that he was searched and no weapons were found. The incident is still under investigation and no charges have been laid.

Prior to the arrest, a crowd had gathered at the memorial, leaving flowers, candles, flags and cards for the soldier who was fatally shot at the location.

A group of MPs including the prime minister gathered along the perimeter of the shooting scene to pay their respects before heading to the House of Commons.

Prime Minister Stephen Harper and his wife Laureen left a wreath at the edge of the yellow police tape surrounding the area.

MPs huddled together and sang 'O Canada' before hugging and wiping away tears. New Democrat MP Mike Sullivan passed out Canadian flag pins to those who had gathered in the location.

After the anthem, NDP MP Charlie Angus was heard saying, "Let's get back to work."

In a message on Twitter, he wrote: "We will not be intimidated. Democracy goes on."

The group headed into the House of Commons in time for the usual 10 a.m. session, but held a moment of silence before getting on with the session.

An hour after Parliament resumed, a group of senators visited the memorial to pay respects. Groups of military officers were also seen at the site on Thursday morning.

Opposition Leader Thomas Mulcair and his wife, Catherine Pinhas, laid a wreath at the scene during the noon hour.

Cpl. Nathan Cirillo, 24, was fatally wounded while standing guard at the Tomb of the Unknown Soldier shortly before 10 a.m. Evidence markers are still placed where the soldier fell.

Flags at Parliament Hill and other federal buildings are being flown at half-mast in honour of Cpl. Cirillo and Warrant Officer Patrice Vincent, who died in after a hit-and-run attack in Quebec on Monday.