As enrollment surged on the final day of open enrollment under the Affordable Care Act, federal officials extended their early-morning maintenance window to correct a software problem.

Technical support for the site regularly installs fixes between 1 a.m. and 5 a.m.; this time the team kept the site down for longer, prompting widespread concern that the system had crashed. Centers for Medicare and Medicaid Services spokesman Aaron Albright wrote in an e-mail at 8:14 a.m. that it was back online.

" marketplace application and enrollment system is coming online now," he wrote. "The tech team extended regular maintenance window this morning and is bringing the system online gradually to best meet consumer demand."

The Web site, which experienced major problems after it launched on Oct. 1, has been working better in the past few months. But even senior administration officials said this month it was hard to predict how it would handle the expected deluge of traffic as many Americans sought to begin the enrollment process before it ends Monday at midnight.

In the past week, has received more than 8.7 million visits, including 2 million this past weekend.

The tech team corrected the software bug, according to an administration official, and consumers who could not access the site but left their e-mail as part of a queueing system will be invited back to sign up for insurance.