The data hub behind the Obamacare website was "experiencing an outage" on Tuesday night, state and federal officials said, prohibiting customers from submitting new applications.
Verizon, which provides some technology services behind HealthCare.gov, said federal officials asked the company to provide additional computing and storage ability.
"At the request of HHS's deputy CIO, we are now undertaking infrastructure maintenance, which should be complete overnight," spokesman Jeffrey Nelson said. "We anticipate the strengthened infrastructure will help eliminate application downtimes."
An official with the agency that oversees HealthCare.gov acknowledged the systems outage, and said the website would be brought back online when maintenance was complete.
A spokeswoman from the Connecticut state exchange said the outage was preventing users from completing the full registration process, but some functions were still working.
Verizon had no immediate response to questions about how customers using the site would be impacted.
On Sunday, an outage traced back to Verizon left customers unable to apply for coverage. The snafu affected the federally-run HealthCare.gov and more a dozen state-run sites. Fourteen states and the District of Columbia are running their own insurance marketplaces; the other 36 states use the federal exchange.
Since going live on Oct. 1, major issues with HealthCare.gov have prevented people from registering and applying for coverage.
Marilyn Tavenner, head of the government agency overseeing the site, told lawmakers at a hearing that the massive issues were a "surprise" and "did not show up in testing."
"We know that consumers are eager to purchase this coverage and to the millions of Americans who have attempted to use HealthCare.gov to shop and enroll in health care coverage, I want to apologize to you that the website has not worked as well as it should," she said.
President Obama said technical teams were "working out the kinks in the system," and a former White House official he appointed to oversee the repairs said the site would be working for "vast majority" of users next month.
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