WASHINGTON - Nearly six million Americans so far have enrolled in insurance for 2016 through HealthCare.gov, President Obama announced on Friday, touting a big increase over last year that he said shows the Affordable Care Act is succeeding.

The number who have already signed up on the federal insurance exchange compares with 3.4 million at the same stage a year ago and comes at a significant moment in the ACA's enrollment cycle: the deadline for people who want health plans in place starting on New Year's Day. The figures also show that 2.4 million of the current total are new customers, about a third more than at this point last year.

This good news for proponents of the health-care law, popularly known as Obamacare, prompted the White House to catapult it from what are normally routine announcements by federal health officials to the opening of a presidential news conference.

"The more who sign up, the stronger the system becomes," Obama said at his final news conference of the year.

Earlier in the week, federal health officials signaled that interest in HealthCare.gov was running high. They granted a 48-hour extension to the original Dec. 15 deadline for obtaining insurance for Jan. 1, saying that the volume was so great that about one million people had been placed in waiting lines to reach federal call centers or use the enrollment website.

That surge occurred even though the administration recently tamped down public expectations for how many additional consumers are likely to get ACA insurance for the coming year.

This fall, Health and Human Services Secretary Sylvia Mathews Burwell issued a forecast that 10 million people will be covered through such health plans by the end of 2016 - only slightly more than expected for the end of this month. Burwell also has said that enrollment marketing efforts this year would focus on a cadre of 10.5 uninsured people who are eligible to sign up on the exchanges, intended for those without access to affordable insurance through an employer. HHS has forecast that one-quarter to one-third of them would enroll, which means that the 2.4 million new customers to date are already approaching that prediction.

The common wisdom has been that attracting new customers to HealthCare.gov would be more difficult in this third year, because people still uninsured have rejected two previous opportunities to gain coverage. On the other hand, the health-care law requires most U.S. residents to carry insurance, and penalties next year will rise to $695 per person or 2 percent of income.

The figures announced by the president, and additional detail provided by federal health officials, reflect activity in 38 states that are now relying on HealthCare.gov. They exclude the dozen states, plus the District of Columbia, that operate separate insurance marketplaces under the ACA.