Sign-ups under President Barack Obama's health care law surged last week, driven by a deadline for getting covered by Jan. 1, officials said Tuesday. Unlike last year, the HealthCare.gov website was working well.

More than 1 million people picked a plan from Dec. 6 through Dec. 12, bringing the total to nearly 2.5 million, said Health and Human Services officials.

"It's been a strong start," said Andy Slavitt, overseeing the second year rollout. "Our call center and our technology have done their jobs -- so far."

Tuesday's numbers were partial, really just a subtotal. They reflected the 37 states served by HealthCare.gov. Enrollment for states running their own websites will be reported later. And Tuesday's numbers also did not include totals from the weekend and Monday, which saw strong consumer interest.

The administration has set an overall goal of 9.1 million people signed up for 2015. That includes new customers plus roughly 6.7 million current customers, most of whom will be renewed automatically.

That goal could well be exceeded after this year's promising start.

Indeed, Avalere Health, a private market analysis firm, estimated Tuesday that enrollment will total 10.5 million people by the end of 2015. That's still lower than the 13 million that congressional budget analysts have projected.

Obama's law offers subsidized private insurance to people who don't have access to coverage through their jobs. Sign-up season runs through Feb. 15, but Monday was the deadline for most people to pick a new plan, or switch existing coverage, in time for the start of 2015.

The federal call center experienced long telephone hold times this weekend under the deadline crunch. About 500,000 people left their phone numbers for callbacks. HealthCare.gov had to deploy its online waiting room for some customers on Monday, but it had no major problems. Last year, the website was prone to crashing.

"If we put last year and this year together, they have done an amazing job at ramping up their systems," said Mehdi Daoudi, CEO of Catchpoint Systems, which monitors website performance. "The fact is they have been able to adapt."

Cathpoint analyzed HealthCare.gov's performance from Nov. 26 through noon Monday at the request of The Associated Press. The study was conducted with a mix of computers, using a cross-section of Internet providers, at locations around the country.

It found that HealthCare.gov's overall availability and user response time were good, and that the website improved notably in some areas.

For example, logging in and logging out is much faster. Last year the median, or midpoint, time for logging in was 18.46 seconds. For logging out, it was 4.61 seconds. This year the median login time was 3.21 seconds, and 1.91 seconds to log out. The log-in page was available more than 95 percent of the time this year, compared to 84 percent last year.

But it's too soon for a victory lap at the White House.

The next big logistical challenge is making sure that millions of current customers will have a smooth transition to 2015. Existing coverage is supposed to renew seamlessly, but it's the first time the government has attempted the transition.

There's special concern over several hundred thousand people whose current plans will not be offered next year. The government says it will automatically re-assign them to similar coverage.

The health insurance industry announced Tuesday it will help smooth the transition.

The trade group America's Health Insurance Plans said insurers will give customers more time to pay their premiums for January, and will promptly refund any overpayments by consumers who switched plans and may have gotten double-billed by mistake. Insurers also plan to help customers who have problems filling prescriptions or getting medical care at the start of the year.