More than 15 million people have signed up for health insurance plans offered on the Affordable Care Act’s federal marketplace, a 33 percent increase compared with the same time last year, according to preliminary data released by the Biden administration Wednesday.

Federal health officials project that more than 19 million people will enroll in 2024 coverage by the end of the current enrollment period next month. That total would include those who gain coverage through state marketplaces, continuing the record-setting pace.

“It means more Americans have the peace of mind of knowing that going to the doctor won’t empty their bank account,’’ Xavier Becerra, the health and human services secretary, said in a statement.

Despite a recent warning from former president Donald Trump, the front-runner in the race for the 2024 Republican presidential nomination, that he was “seriously looking at alternatives’’ to the Affordable Care Act, the latest surge in marketplace enrollment is a testament to the law’s enduring power.

Legislation passed earlier in the COVID-19 pandemic increased federal subsidies for people buying plans, lowering the costs for many Americans. The Biden administration also lengthened the sign-up period and increased advertising for the program and funding for so-called navigators who help people enroll.

“More and more people are realizing they can come onto the marketplace,’’ said Cynthia Cox, the director of the Program on the Affordable Care Act at KFF, a nonprofit health policy research group.

She added, “Just because the ACA has been around for a while doesn’t mean people who need to sign up for it know how to do that.’’

On Dec. 15 — the deadline to sign up for coverage that begins Jan. 1 — nearly 750,000 people opted for a marketplace plan on HealthCare.gov. It was the largest single-day total yet.

Dr. Benjamin Sommers, a health economist at Harvard University who served in the Biden administration, said that improved outreach helped explain the record sign-ups. “I’m pleasantly surprised,’’ he said.

With years of increased subsidies, he added, “it might be this is the natural growth rate over a few years in a new policy environment.’’

Kody Kinsley, the top health official in North Carolina, said that his state had gotten creative by using its efforts expanding Medicaid to also sign people up for marketplace plans.

“We’ve had a very broad educational and outreach campaign — with civic organizations, churches, navigators — built around expansion to educate folks about eligibility,’’ he said in a text message.

He added, “As part of that, we support folks to get coverage on the marketplace if they’re not eligible’’ for Medicaid.