Update 8:30 a.m.: HealthCare.gov appears to be back online.
HealthCare.gov was unavailable Monday morning as the clock wound down to the deadline for signing up for health coverage.
The Department of Health and Human Services was aware of the issue and was working to bring the system back online as soon as possible, according to a statement obtained by NBC News.
Administration officials confirmed last week that six million Americans had already enrolled in private health coverage under Obamacare. The official deadline for open enrollment is Monday at midnight ET, but the Obama administration announced that extra time would be granted to those who started applying for health insurance and were unable to finish before the enrollment deadline.