Americans seeking to purchase health insurance through the new Obamacare exchanges for coverage to begin Jan. 1 will have more time to do so.

The Department of Health and Human Services announced today that the deadline to apply for Jan. 1 coverage will be extended by one week, from Dec. 15 to Dec. 23. That means applications filed through the exchanges during that additional week will be eligible for coverage to begin at the start of 2014.

We are having "ongoing conversations with issuers. They're aware of the date change. This was done in consultation with them," Centers for Medicare and Medicaid Services spokeswoman Julie Bataille told reporters on a conference call. Insurers, however, said nothing has yet been put in writing though they expect the change is mandatory.

"It makes it more challenging to process enrollments in time for coverage to begin on January 1," Robert Zirkelbach, spokesman for industry group America's Health Insurance Plans, told ABC News. "Ultimately it will depend on how many people enroll in those last few days."

Consumers who select a plan through the exchanges and want their coverage to begin on Jan. 1 must pay the first month's premium on or before Dec. 31, officials said.

The enrollment period for the Obamacare exchanges will remain open through March 31 for coverage in 2014. The new deadline is simply for those wanting coverage on the first possible day. HHS has so far ruled out an extension of the overall period.

Meanwhile, Jeff Zients, the Obama administration official overseeing repairs to HealthCare.gov, said today that "measurable progress" is being made to improve the system and that workers are "on track" to resolve capacity shortfalls and a flawed user experience in nine days.

Zients said the website can handle about 25,000 concurrent users, half its intended capacity. But he promised that come Dec. 1, it will be able to handle 50,000 users at the same time.

"By the end of the month, the system will be able to accommodate 800,000 visits a day from consumers seeking information, filling out applications, shopping and enrolling," he said.

"The vast majority of users will not experience error messages or slow response times," Zients added. "The system will not work perfectly, but it will operate smoothly for the vast majority of users."