A combination of high demand and technical glitches seemed to overwhelm the online system early in the day. Federal and state officials were working to address the problems, which led to long waits on government websites and a federal call center.
As a sign of how ready Americans were to get started, Obama said more than 1 million people had visited the government's main website before 7 a.m. EDT — exceeding expectations and contributing to the delays.
In Obama's home state, dozens of people who came to a Champaign, Ill., public health office to sign up for coverage found computer screens around the room flashing an error message: "System is unavailable."
Kimberly Shockley — logging in from Houston, Texas — and Mike Weaver, who lives in rural southern Illinois, ran into similar glitches: They could not get past the security questions while trying to set up their personal accounts through healthcare.gov.
"I'm frustrated, very frustrated," said Shockley, a self-employed CPA. She spent more than an hour trying to get the security questions to work Tuesday morning without success. When she clicked on a drop-down menu of suggested security questions, none appeared. She then tried to create her own questions, but that didn't work either.
Weaver, a self-employed photographer, said he also ran into problems with the drop-down menus. And when they started working, he still wasn't able to set up his account.
"The first day of something that you know is going to have a lot of bugs, it's not that frustrating," he said. "If it was the last day to sign up ... then I'd be terribly frustrated."
Shockley has health insurance, but is looking for a better plan. Weaver is uninsured.
State-operated sites also experienced glitches. Rhode Island's site opened as scheduled, but was quickly overwhelmed by visitors and went down. A spokesman for the New York Department of Health blamed problems with the 2 million visits to the website in the first 90 minutes after its launch. Washington state's marketplace used Twitter to thank users for their patience.
Exchange officials in Colorado said their website would not be fully functional for the first month, although consumers will be able to get help applying for government subsidies during that time. Hawaii's marketplace wasn't allowing people to compare plans and prices.
Connecticut seemed to be a bright spot, although some users reported problems. Access Health CT sent out a tweet shortly before noon Tuesday, confirming the marketplace logged 10,000 visitors in the first three hours of operation and 22 enrollments. A family of three was the first to sign up for coverage.
California, home to 15 percent of the nation's uninsured, reported delays online and on the phone because of heavy volume. The first completed health insurance application was taken at 8:04 a.m., just minutes after the exchange opened, an official there said.
In Portsmouth, N.H., Deborah Lielasus tried to sign up for coverage but got only as far as creating an account before the website stopped working. She said she expected glitches.
Lielasus, a 54-year-old self-employed grant writer, currently spends about $8,500 a year in premiums and more than $10,000 for out-of-pocket expenses because she has a health condition and her only option has been a state high-risk insurance pool. She said she expects those costs to decrease significantly.
As excited as she was to sign up, she said, her anticipation was tempered by dismay over the government shutdown that was led by congressional Republicans who want to block the health insurance reforms.
"I'm really happy that this is happening, that this is being launched ... I feel like it's a child caught in the middle of a really bad divorce," Lielasus said.
The shutdown will have no immediate effect on the insurance marketplaces that are the backbone of the law, because they operate with money that isn't subject to the annual budget wrangling in Washington.
The marketplaces represent a turning point in the nation's approach to health care, the biggest expansion in coverage in nearly 50 years.
The Obama administration hopes to sign up 7 million people during the first year and aims to eventually sign up at least half of the nearly 50 million uninsured Americans through an expansion of Medicaid or government-subsidized plans.
But if people become frustrated with the malfunctions in the computer-based enrollment process and turn away from the program, the prospects for Obama's signature domestic policy achievement could dim.
"You've got to launch this thing right the first time," said Robert Laszewski, a consultant who worked 20 years in the insurance industry. "If you don't, financially you will never recover."
Neera Tanden, president of the Center for American Progress, which helped work for passage of the law, cautioned against rushing to judge on first-day performance. Numerous observers had predicted bugs and setbacks. Trained outreach workers in many states are having trouble getting the certification they need to start helping people to enroll.
In Texas, a federally funded network of "navigators" hired to help residents enroll was off to a rocky start Tuesday because of backtracking participants — including some cowed by the politics of the health law.
At least four regional government councils — covering more than 30 counties statewide — reversed course in the past two weeks and turned away funds that would train navigators in their areas. Local leaders described their hesitancy as a mix of uncertainty surrounding state rules and a fear of running afoul of Republican leaders.
Many states predicted that an initial surge of interest would test the online system, but they expect most people to sign up closer to Dec. 15, which is the deadline for coverage to start Jan. 1. Customers have until the end of March to sign up in order to avoid tax penalties.
Under the law, health insurance companies can no longer deny coverage to someone with a pre-existing medical condition and cannot impose lifetime caps on coverage. They also must cover a list of essential services, ranging from mental health treatment to maternity care.