Visitors to the healthcare.gov website Friday morning saw a message saying the system was receiving scheduled maintenance, CNN reported. The site was back up by midafternoon.
The exchange's technical team encountered an error during routine maintenance Thursday night, said Joanne Peters, a Department of Health and Human Services spokeswoman.
The outage occurred close to Monday's deadline for customers in the states using the federal exchange to choose a plan on the website to be eligible for coverage beginning Jan. 1.
Thursday the White House announced individual policy holders who received termination notices could qualify for hardship exemptions and buy catastrophic plans on the exchange, a moved denounced by the U.S. health insurance industry.
The industry said the surprise announcement upends assumptions insurance carriers made when setting premiums for 2014.
"This latest rule change could cause significant instability in the marketplace and lead to further confusion and disruption for consumers," said Karen Ignagni, president of America's Health Insurance Plans, the industry's national political advocacy and trade association.
The new rule will let any consumer whose current, substandard insurance plan is being canceled claim a "hardship exemption" and buy a bare-bones "catastrophic plan" if standard health plans sold through the new federal and state marketplaces are more expensive than their previous plan.
"This is a common sense clarification of the law," Peters said. "For the limited number of consumers whose plans have been canceled and are seeking coverage, this is one more option."
HHS Secretary Kathleen Sebelius said the goal was to ensure "the smoothest possible transition" for people seeking new coverage after cancellation of their policies.
Sebelius' department issued a bulletin late Thursday advising consumers, "If you have been notified that your individual market policy will not be renewed, you will be eligible for a hardship exemption and will be able to enroll in catastrophic coverage."
Catastrophic plans were previously limited, under the Patient Protection and Affordable Care Act, or "Obamacare," to people less than 30 years of age or those who qualified for a set of specific hardship exemptions.
But now, under the broadened definition of hardship, people who buy catastrophic plans will be exempt from the penalty imposed on many Americans who don't have coverage starting in 2014.
HHS said it was setting up a hotline, at 1-866-837-0677, for people who got cancellations and wanted to take advantage of the new option.
It was not immediately clear how many people might qualify under such an arrangement. The administration said Thursday it believed fewer than 500,000 people whose existing coverage had been terminated and hadn't yet enrolled in another plan.