WASHINGTON – President Donald Trump's suggestion for fighting the massive Notre Dame fire did not get good reviews.

Tweeting that it was "so horrible to watch the massive fire at Notre Dame Cathedral in Paris," Trump added: "Perhaps flying water tankers could be used to put it out. Must act quickly!"

Professional firefighters called Trump's proposal impractical at best. Deploying the kinds of airplanes used to fight forest fires would be dangerous in an urban area, they said, noting that force of the water could knock the building down and threaten firefighters on the ground.

"The drop of water by air on this type of building could indeed result in the collapse of the entire structure," the French government civil defense agency tweeted.

It later tweeted out a statement in English, in an apparent response to Trump, saying that "hundreds of firemen of the Paris Fire Brigade are doing everything they can to bring the terrible #NotreDame fire under control. All means are being used, except for water-bombing aircrafts which, if used, could lead to the collapse of the entire structure of the cathedral."

The French newspaper Le Monde derided Trump's plan as "impossible."

Critics on Twitter called Trump's comment the epitome of second-guessing in the middle of a disaster.

"Thanks Fire Chief Bill," tweeted Michael Cohen, a Boston Globe columnist.

More:'Everything is burning': Famed Notre Dame cathedral ablaze in Paris

Later, during a roundtable discussion on the economy and tax reform in Minnesota, Trump called Notre Dame "one of the great treasures of the world," and said it "looks like it's burning to the ground."

Before giving remarks on the economy, Trump said of the fire: "That puts a damper on what we're about to say."

Air tankers are brought in to fight wildfires that are spread over a wide area, and are often brought in hours or even days after the event starts.

Wayne McPartland, a retired New York City Fire Department battalion chief, told CNBC that aerial tankers are not the answer at Notre Dame.

“If you hit that with tons of water from above, that’s going to collapse the entire structure and make the situation worse,” McPartland said. “If you miss, you might hit civilians in the street.”