CBS "Late Show" host Stephen Colbert blasted President Trump's response to the coronavirus Monday night, describing Trump as a "monster" for comparing the number of coronavirus casualties to deaths from the flu.

"So last year 37,000 Americans died from the common Flu," Trump tweeted Monday morning. "It averages between 27,000 and 70,000 per year. Nothing is shut down, life & the economy go on. At this moment there are 546 confirmed cases of CoronaVirus, with 22 deaths. Think about that!"

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"Ok, let me think about that," Colbert responded mockingly during that night's monologue. "You're a monster."

The host cracked that the coronavirus was the "first crisis of Trump's presidency that he did not cause himself" and took issue with Trump golfing in Florida over last weekend.

Colbert added, however, that when Trump "hunkers down and focuses on the problem, that's when he really sucks."

The World Health Organization declared Wednesday that the coronavirus outbreak is now a pandemic. The organization expressed alarm both about mounting infections and inadequate government responses but added that it’s not too late for countries to act.

By reversing course and using the charged word “pandemic” that it had previously shied away from, the U.N. health agency sought to shock lethargic countries into pulling out all the stops. Trump said on Wednesday that his coronavirus task force was "working around the clock."

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"Together we are putting into policy a plan to prevent, detect, treat and create a vaccine against CoronaVirus to save lives in America and the world. America will get it done!" he tweeted.

According to the WHO, people with mild illness from the virus recover in about two weeks, while those with more severe illness may take three to six weeks to recover.

The Associated Press contributed to this report.