The company that operates HealthCare.gov experienced a connectivity glitch on Sunday, another complication for an already beleaguered population of would-be health care applicants.
White House officials said the company that operates the hub, Terremark, was working to resolve the issue as quickly as possible.
Health and Human Services spokesman Joanne Peters said in a statement that the website was down because the company "experienced a failure in a networking component, and planned maintenance to replace it brought down network connectivity to the data center."
"Our understanding is that this failure is likely impacting several other sites, in addition to HealthCare.gov and the Data Services Hub," she added.
The Oct. 1 launch of Obama's health care law, also known as Obamacare, has been marred by technical glitches and delays.
The department has encouraged website users to contact their call center to apply for coverage.
NBC's Kristen Welker and Reuters contributed to this report.