The Centers for Medicare and Medicaid Services (CMS) said it is replacing data center services from Verizon Communications Inc's Terremark subsidiary, with services from Hewlett-Packard Co.

Terremark's data center experienced issues in late October that caused outages across the system, prompting embattled Health and Human Services Secretary Kathleen Sebelius to phone Verizon's chief executive to discuss the problems.

Obama and Sebelius had promised the website would make it easy to shop for health insurance required under the 2010 Affordable Care Act, commonly known as Obamacare.

Instead, slow response times, error messages and outages like the ones seen at Terremark's data center meant few Americans have been able to enroll so far.

The disaster has fueled Republican criticism of the law, and alarmed Democrats who supported it. The administration has had to scramble to make fixes in the hopes enough Americans sign up by deadlines in December and March.

Both Verizon and HP declined comment on the contract change, as did the White House, which referred questions about the contract to CMS.

CMS said its contract with Terremark had been set to end in March 2014. Last summer, several months before the botched October 1 launch of HealthCare.gov, the agency issued a "task order" asking for bids. HP was awarded that contract, a CMS spokesman said in a statement.

The contract change was first reported by the Wall Street Journal.

Now, CMS needs to transition its data center to HP at a time when it is just beginning to dig out from a mountain of problems with the website, which is designed to let consumers shop for health insurance required under Obama's signature health care law.

The complexity of the switch between data center providers could be an additional challenge for the project. A CMS spokesman did not respond to questions about whether the transition would affect the website.

The Obama administration has said it plans to have the website working smoothly for most users by this weekend.

Part of that upgrade involves doubling capacity so the website can handle 50,000 users at once.

A source close to the project, who spoke on condition of anonymity, said there are some concerns about the website's ability to handle so many users because of problems with switches and servers maintained by Terremark.

"CMS has begun the necessary activities to transition the data center over to HP. We are working to ensure a smooth transition between the two contractors," the CMS spokesman said in a statement.

Verizon has received $55.4 million for its work on the healthcare marketplaces since its contract started in 2011, according to federal contracting records.