The US government launched the centrepiece of President Barack Obama’s landmark healthcare reform yesterday, opening online insurance marketplaces across the country for millions of uninsured Americans, but technical glitches prevented early access for many.

The first day of the six-month open enrolment period on the state marketplaces, or exchanges, went ahead despite a partial federal government shutdown precipitated by Republican opposition to the healthcare law that deadlocked a spending bill in Congress.

According to early checks, the rollout of the most ambitious US social programme in five decades had a rocky start. A federally-run exchange for consumers in 36 states began posting error messages for at least 25 of them soon after the system opened for enrolment at 8am EDT (2pm Central European time), citing online traffic as a reason for the difficulties.

An Obama administration official said experts were aware of the issue and were working on it. The Department of Health and Human Services directed consumers to call centres and local community organisers to seek information.

Frustrated customers are likely to fuel opposition to the healthcare law from Republicans in the US House of Representatives, who have voted more than 40 times to repeal it.

“It’s very significant for the political campaign but not for the enrolment campaign,” said Jon Kingsdale, the former head of the Massachusetts state health exchange, which opened in 2006 and became the model for Obamacare.

“I don’t know if it’s two weeks or five weeks, but I don’t think we’re talking just days,” Kingsdale said. He said if the problems persist until November, “that is really a big problem.”

The websites will give many Americans their first glimpse of new subsidized health plans that are being offered to millions of the uninsured, in the most ambitious US social programme since Medicare was introduced in the 1960s.