Newark, New Jersey (CNN) Sylvia Mathews Burwell is issuing a grave warning to Republicans: Repealing Obamacare will result in "chaos."

Burwell, President Barack Obama's secretary of Health and Human Services, told CNN Wednesday that dismantling the Affordable Care Act will hit millions of Americans' healthcare coverage, result in a spike in premiums and unleash widespread uncertainty across the insurance market.

The secretary's sober remarks came five weeks after Donald Trump's Election Night victory — an unexpected outcome that has suddenly handed the Republican Party an opening to overhaul Obama's signature policy accomplishment. In anticipation of Trump's inauguration on January 20, GOP lawmakers are preparing to vote to repeal key portions of Obamacare early next month.

"If there is repeal, there would be chaos," Burwell said in an interview at a diner in Newark, New Jersey. "If your child is on your policy 'til 26, and it's repealed, that goes away. If you have a pre-existing condition -- asthma, cancer, diabetes, high blood pressure, any of those things -- you could be kept off of insurance if you had to make a move or a transition or were unemployed for a portion of time."

She added: "The 20 million folks who have gotten insurance -- that would go away too."

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