Prime Minister Justin Trudeau says his "heart breaks" for those impacted by the "horrific" shooting at an elementary school in Texas that killed 21 people on Tuesday.

"The students, the parents, the teachers, the entire community have had their lives changed forever by this unimaginable event," Trudeau told reporters in Vancouver on Tuesday.

"All of Canada grieves with our American friends in this terrible, terrible day."

Officials say an 18-year-old gunman killed 19 children and two adults as he went from classroom to classroom at Robb Elementary School in the town of Uvalde, a heavily Latino town about 135 kilometres west of San Antonio. The shooter was later killed by law enforcement.

“As a parent, I’m going to have to go home to my kids, including my eight year old, and talk to them again about the inexplicable school shooting that we saw in the United States,” Trudeau said.

He mentioned that he used to be a teacher himself, and that he is thinking of the trauma that students, parents and teachers must be going through in Texas right now. 

Reacting to news of the attack, NDP Leader Jagmeet Singh took to Twitter on Tuesday to say that he is heartbroken like "so many."

"Children deserve more than thoughts and prayers. They deserve protection and safety. They deserve life," he tweeted.

Marco Mendicino, minister of public safety, called it “the type of news that just stops us all cold in our tracks.”

Speaking Wednesday in Halifax, he told press that when this type of tragedy occurs, he thinks of how important the “work that we do as parliamentarians” is.

“I think about the young people that we are here to represent and protect,” he said.

“The harsh reality of the matter is that there are no words that can sufficiently do justice to the pain and the anguish and the devastation that the families and that community feels this morning.” 

Bloc Quebecois Leader Yves-Francois Blanchet said Wednesday morning his thoughts are with those families affected by the tragedy in Texas.

"The arms trade - sordid when it comes to smuggling - and the protection of very personal privileges must no longer be used as collateral for heart-breaking scenes," he wrote in French on Twitter.

Tuesday's assault marks the deadliest shooting in a U.S. school since the Sandy Hook Elementary massacre in Newtown, Conn., in December 2012, which killed 20 children and six adults, and has reignited calls for greater gun control in that country.

The shooting also comes just 10 days after a gunman in body armour killed 10 Black shoppers and workers at a supermarket in Buffalo, New York, in what authorities have since deemed a racist attack.

Speaking from the White House Tuesday, just hours after the shooting in Uvalde, U.S. President Joe Biden called for new restrictions on firearms.

"I am sick and tired of it," he said. "We have to act. And don't tell me we can't have an impact on this carnage."

Although calls for greater gun control in the U.S. have resurfaced numerous times after the country has suffered through mass shooting after mass shooting, those campaigns have made little progress thus far.

In the wake of this latest mass shooting, Trudeau reiterated Canada’s efforts to control access to guns.

“As a government over the past years, we have stepped up significantly on keeping Canadians safe,” he said. "We just recently further strengthened background check requirements for purchasing firearms in Canada. Last year we banned military style assault weapons, which are now illegal to buy, to sell, or to use anywhere in Canada. And we’ve committed to moving forward on doing even more.”

Mendicino added that Canadians need to remember that these tragedies can and do happen here as well.

“We still have a lot of work to do ourselves here in Canada,” he said. “We’re not immune from the kind of gun violence that sadly has afflicted many communities here.” 

With files from The Associated Press