Thousands gathered in Ottawa on Friday to commemorate Canada's longest ever military engagement, in Afghanistan.

With a marching band, a Chinook helicopter and Leopard tanks parked on parliament's front lawn, a memorial in the Senate chamber, a 21-gun salute, a fly-by and the presentation to the governor general of the last Canadian flag to fly in Afghanistan, Canadians paid tribute to their military.

"This mission, started the 11th of September 2001 with the death of 24 Canadians in the attacks on the World Trade Centre (in New York), has been long," Prime Minister Stephen Harper said in a speech.

"And it has been hard," he added.

"This National Day of Honour, the first of its kind in Canadian history, is an unprecedented opportunity for us to say thank you to the men and women who have fought and have served for Canada.

"We are here today to honor their dedication, to honor their heroism, and to honor their sacrifice."

Canada initially committed troops to Afghanistan in December 2001, and until 2011 was involved in heavy fighting against Taliban militants in the violent south of the country.

From 2011 to 2014, Canadian troops took on training the Afghan military and police.

In all, 40,000 Canadian troops were deployed to the war-torn country. The last returned home in March.

A Canadian diplomat, a journalist, two civilian contractors and 158 soldiers were killed in the conflict.

More than 2,000 Canadian soldiers were also wounded.