(Reuters) - Wall Street's main stock indexes tumbled late Monday to end sharply lower after President Donald Trump announced the start of 25% tariffs on Canada and Mexico.

Trump said on Monday that there was no chance for Mexico or Canada to prevent 25% tariffs from taking effect on Tuesday.

"They're going to have to have a tariff. So what they have to do is build their car plants, frankly, and other things in the United States, in which case they have no tariffs," Trump said at the White House.

The S&P 500 lost 1.75%, to end at 5,850.31 points, while the Nasdaq Composite lost 2.64%, closing at 18,350.19. The Dow Jones Industrial Average fell 1.47%, to 43,197.30.

The Canadian dollar and Mexican Peso each fell to a one month low against the U.S. dollar.

COMMENTS:

THOMAS MARTIN, SENIOR PORTFOLIO MANAGER, GLOBALT INVESTMENTS, ATLANTA GEORGIA

"It seems that tariffs are definitely going to go through and it increases the chances of a real economic fallout. The markets are not psyched to stick around for that"

"To say 'no room' for negotiation is a hard line, a definitive statement. So markets are saying 'maybe Trump will do implement tariffs. It's just increasing the probability of a worse outcome. So asset managers want to be out (of stocks) and see how things transpire"

TIM GHRISKEY, SENIOR PORTFOLIO STRATEGIST, INGALLS & SNYDER NEW YORK

"This really in Trump's hands, the fact that he's basically saying he's going to put tariffs on Canada and Mexico and there's nothing they can do about it."

"This is a bit of a meltdown here. And I think the pressure's on Trump to stop it. But I don't know if that's in his DNA or not."

"I think we've all been taught that nobody wins in a tariff war, and Trump's basically saying it's going to happen no matter what."

"And I don't see how that solves anything."

"You know, unless he backs away from the from this tariff war it can hit all sorts of industries.

"We rely on commerce with Canada and with Mexico. You just can't flip a switch and all of a sudden replace that with production from the U.S."

"It's really short sighted of Trump. This whole tariff war, I don't think it solves anything or helps anybody."

PETER TUZ, PRESIDENT, CHASE INVESTMENT COUNSEL, CHARLOTTSEVILLE, VIRGINIA

"Today the realization hit some people that tomorrow we will see tariffs. That brings with it uncertainty as far as the earnings of some companies as well as the overall direction of the U.S. economy. I think there was some hope that before they were implemented there would be deals struck with the affected parties and we wouldn't see them."

"We're kind of going into a brave new world here of tariffs on several countries and it's just really hard to determine two things: the reaction of the U.S. consumer to tariffs, and the earnings and results of companies that will be affected by the tariffs. So I think the world is taking a step back and is going to re-evaluate as appropriate."

(Compiled by the Global Finance & Markets Breaking News team)