U.S. President Barack Obama announced on Thursday that 8 million people have signed up for health insurance under the Affordable Care Act, known as the Obamacare and 35 percent of them are under the age of 35, which have surpassed previous projections about the program's first year performance.

Speaking at a televised White House press conference, Obama said his signature healthcare law is now covering more people with affordable health insurance "than most would have predicted just a few months ago."

He said 8 million Americans have purchased private insurance in the health insurance marketplaces under the Obamacare since their launch last October.

"Independent experts now estimate that millions of Americans who were uninsured have gained coverage this year, with millions more to come next year and the year after," Obama said, adding that the healthcare reform is bringing economic security to more Americans and adding competition to the individual market.

Obama noted that 35 percent of people who enrolled through the federal marketplace are under the age of 35, just short of the Obama Administration's goal of 38 percent. According to a fact sheet released by the White House, 28 percent of the enrollees are between 18 and 34 years old.

The latest figures show a good sign that the Obamacare is able to attract young adults into the insurance pool.

The president also seized the opportunity to target Republicans who have long been opposing to the Obamacare, accusing them of their "endless, fruitless repeal effort" against the healthcare overhaul.

"The point is, the repeal debate is and should be over. The Affordable Care Act is working. I know the American people don't want us to spend the next two-and-a-half years fighting settled battles," Obama told reporters.

The latest good news comes after a disastrous rollout of the Obamacare last October, when the federally-run online marketplace for uninsured Americans to pick up an insurance plan failed and have stirred up months of criticism and controversy.

The Obama administration hoped the latest better-than-expected enrollment data could reassure Democrats that they will not be further burdened by the rocky rollout of the Obamacare in the mid- term elections this year.

Kathleen Sebelius resigned last week as the Secretary of Health and Human Services, which has been responsible for the marketplaces under the Obamacare. The announcement came just two weeks after the first six-month enrollment period of the Obamacare drew to a close on March 31, which attracted more than 7 million enrollees and met the target.