Republicans blasted the White House on Monday after President Obama’s administration announced premiums for his signature health care law will rise sharply next year and many consumers would be down to just one insurer.

Republican presidential nominee Donald Trump, while campaigning in Tampa, Fla., emphatically declared ObamaCare “over.”

Trump added that his Democratic rival, Hillary Clinton, "wants to double down and make it more expensive and it's not gonna work. ... Our country can't afford it, you can't afford it." He promised his own plan would deliver "great health care at a fraction of the cost."

GERRI WILLIS: OBAMACARE ENDGAME APPEARS

Trump’s running mate Indiana Gov. Mike Pence echoed his partner’s words, saying on Twitter “Higher premiums, less competition & fewer choices lie ahead for ObamaCare. Hillary Clinton wants more of the same.”

Before taxpayer-provided subsidies, premiums for a midlevel benchmark plan will increase an average of 25 percent across the 39 states served by the federally run online market, according to a report from the Department of Health and Human Services. Some states will see much bigger jumps, others less.

Moreover, about 1 in 5 consumers will only have plans from a single insurer to pick from, after major national carriers such as UnitedHealth Group, Humana and Aetna scaled back their roles.

"Consumers will be faced this year with not only big premium increases but also with a declining number of insurers participating, and that will lead to a tumultuous open enrollment period," said Larry Levitt, who tracks the health care law for the nonpartisan Kaiser Family Foundation.

OBAMACARE COLLAPSING BEFORE OUR EYES, SAYS REP.

Speaker Paul Ryan, R-Wis., accused Democrats of only wanting to double-down on ObamaCare instead of fix it and vowed that Republicans would “replace it with real, patient-centered solutions that fit your needs and your budget.”

“The president recently compared ObamaCare to a Samsung Galaxy Note 7, and he's right: this disastrous law is blowing up. But at least you can return the phone,” Ryan added.

Sen. Ben Sasse, R-Neb., urged the White House to admit that the health care law wasn’t working.

"We’ve reached this point because ObamaCare is built on the lie that Washington’s bureaucrats are smart enough to plan health care for millions of Americans. At every turn -- whether it’s CO-OPs collapsing, premiums skyrocketing, or big insurers bailing -- the American people have paid the price. More spin won’t solve this -- it’s time for the White House to admit that this law isn’t working."

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HHS essentially confirmed state-by-state reports that have been coming in for months. Window shopping for plans and premiums is already available through HealthCare.gov.

Administration officials are stressing that subsidies provided under the law, which are designed to rise alongside premiums, will insulate most customers from sticker shock. They add that consumers who are willing to switch to cheaper plans will still be able to find bargains.

"Headline rates are generally rising faster than in previous years," acknowledged HHS spokesman Kevin Griffis. But he added that for most consumers, "headline rates are not what they pay."

The vast majority of the more than 10 million customers who purchase through HealthCare.gov and its state-run counterparts do receive generous financial assistance. "Enrollment is concentrated among very low-income individuals who receive significant government subsidies to reduce premiums and cost-sharing," said Caroline Pearson of the consulting firm Avalere Health

But an estimated 5 million to 7 million people are either not eligible for the income-based assistance, or they buy individual policies outside of the health law's markets, where the subsidies are not available. The administration is urging the latter group to check out HealthCare.gov. The spike in premiums generally does not affect the employer-provided plans that cover most workers and their families.

Overall, it's shaping up to be the most difficult sign-up season since HealthCare.gov launched in 2013 and the computer system froze up.

Enrollment has been lower than initially projected, and insurers say patients turned out to be sicker than expected. Moreover, a complex internal system to help stabilize premiums has not worked as hoped for.

The Associated Press contributed to this report.