Justin Trudeau fell silent for 21 seconds as he was asked about Donald Trump's riot forces reportedly tear-gassing protesters during the US George Floyd demontrations.

In footage that has since gone viral, the Canadian leader is seen pausing for an agonising 21 seconds, appearing to choose his words carefully before he stares down the camera and speaks.

Footage of his silence gripped viewers, as many speculated the Prime Minister was holding his tongue so he could deliver a measured answer.

The two leaders' styles contrast heavily, but Mr Trudeau has followed diplomatic convention of avoiding direct criticism of his counterpart in America, upon which Canada relies heavily for exports.

Canadian Prime Minister Justin Trudeau's prolonged pause stunned viewers

However the leader appeared to struggle to remain neutral as Mr Trump's handling of the protests erupting across the United States draws widespread criticism.

The leader has been accused of egging on the use of force against peaceful protests - as well as violent demonstrations -  in his tweets and speeches.

The Park Police and Trump administration denies using tear gas, in what has become a contentious issue as observers have pointed out seeing police wearing gas masks at the scene, while some reporters found what appeared to be 'OC' cannisters, a type of pepper spray.

The incident moments before Mr Trump read a bible for a photo opportunity drew particularly sharp condemnation in a chaotic week in a United States dually grappling with the coronavirus pandemic and civil unrest over racial discrimination tensions.

Two protesters in Lafayette Park on May 31

Police broke up a peaceful and legal protest in Lafayette Park across from the White House ahead of a speech in the Rose Garden by the president on Monday.

Afterward, Mr Trump walked across the cleared park to make a surprise visit to a church, where he raised a Bible, without making mention of Floyd. 

The protesters are demanding justice over the death of the unarmed black man who died after a policeman pinned him by his neck to the ground for nearly nine minutes in the Minnesota city of Minneapolis.

US President Donald Trump holds up a Bible outside of St John's Episcopal church

Sympathy protests have since been launched across the States and around the world, including in Canada.

Asked about the incident at a news conference, Mr Trudeau was captured taking a long pause before answering, in a silence described variously as 'epic' and 'awkward' on Twitter.

When the Canadian PM finally and haltingly replies, he does so without mentioning Mr Trump directly.

Police form a riot line during the incident in Lafayette Park
The PM stared down news cameras as he chose his words carefully

"We all watch in horror and consternation what's going on in the United States," Trudeau said on Tuesday.

"It is a time to pull people together... it is a time to listen, to learn what injustices continue despite progress over years and decades."

In the speech, he urges Canadians to confront racial inequality in their country too, as he pledges solidarity with the targets of discrimination.