Ontario Premier Kathleen Wynne denounced Donald Trump on Thursday as divisive, a woman hater and blindly protectionist, warning his election as U.S. president would be dangerous for the world.

It was, by far, the harshest condemnation in decades by a senior Canadian politician on U.S. soil of an American presidential candidate in the midst of an election season.

"A candidate who is as misogynist as the Republican nominee, who is blindly protectionist and seems to be uninterested in global collaboration and co-operation would be a very difficult challenge for Ontario and Canada to deal with," Ms. Wynne said in an interview after a day-long visit to Washington that included high-level meetings with senior administration officials.

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While she avoided referring to Mr. Trump by name and declined to say that she was backing Hillary Clinton, the Democratic alternative, she said if Americans elect the Republican nominee, "That outcome would be dangerous."

Ms. Wynne defended her decision to wade into the raucous and bitter U.S. campaign because, she said, "What happens here in a presidential election affects the world; it certainly affects Canada, and it certainly affects Ontario.

"I'm saying what I think," she added, aware that it was unusual, if not unprecedented, for a Canadian premier to publicly denounce a U.S. presidential candidate. It may also be risky: Mr. Trump has vowed to retaliate against foreign politicians who dare attack him.

Mr. Trump's demeanour demands a response, Ms. Wynne said, as do his controversial comments – including vowing to rip up all trade agreements including NAFTA; forcing allies to pay more for defence or refusing to defend them; banning Muslims from entering the United States; and requiring Mexico to pay for a wall along the southern border.

"There's one candidate who is setting out to be divisive and outrageous and to disrupt the normal course of the [political] debate," she said, adding: "It's hard not to have an opinion about what's going on."

She said the election of Mr. Trump would be "destabilizing" and "be very bad for the world, and for Ontario and Canada."

Ms. Wynne's plain-speaking rejection of Mr. Trump's politics of division and isolation echoes the unequivocal criticism by several other major Western political figures. British Prime Minister David Cameron, a Conservative, said Mr. Trump's attitudes toward Muslims and Mexicans were "divisive, stupid and wrong."

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German vice-chancellor and Social Democrat leader Sigmar Gabriel called the Republican nominee a threat to world peace, lumping him with European far rightists. "Donald Trump, Marine le Pen or Geert Wilders – all these right-wing populists are not only a threat to peace and social cohesion, but also to economic development," he said.

Mexican President Enrique Pena Nieto compared Mr. Trump, who infamously called Mexicans "rapists" and "criminals," to the fascists of the 1930s who seized power by stoking fear. "There have been episodes in the history of humanity, unfortunately, where these expressions, this strident rhetoric has only really been [a] very fateful stage in the history of mankind," he said. "That's how Mussolini got in, that's how Hitler got in."

By contrast, Canadian Prime Minister Justin Trudeau has mostly ducked or joked when asked about the current U.S. presidential race.

In a typical equivocating answer, he told the U.S. Chamber of Commerce this spring while in Washington: "I have great faith in the American people and look forward to working with whoever gets elected in November."

Ms. Wynne was in Washington for talks with high-level Obama administration officials and to pitch Ontario as "being ahead of the curve" in developing a low-carbon economy.

Perhaps not surprisingly given the heft Ontario carries in North American trade – far larger than any other Canadian province – she had meetings with a brace of senior U.S. officials, Secretary of Labor Tom Perez and the U.S. Trade Representative Michael Froman.