US Health Secretary Kathleen Sebelius has resigned over the disorderly rollout of US President Barack Obama's controversial Obamacare healthcare law.

Sebelius, who has served as health secretary since Obama's inauguration in 2009, personally made the decision to resign after technical glitches delayed the law's introduction.

The website, which allowed users to register for health insurance, had a series of problems at launch which led to widespread criticism.

However, Obamacare - officially known as the Affordable Care Act - is regarded as one of Obama's stand-out domestic achievements by his supporters.

Sebelius, 65, withstood calls for her to stand down after the website's technical difficulties and Obama kept her in the role despite pressure to relieve her of the senior post.

The frontrunner to replace the former Kansas governor is Sylvia Mathews Burwell, the present budget director, and Obamam is expected to nominate her in the coming days.

Obamacare was introduced in 2010 and its aim is to provide health insurance to the 48 million Americans who are not offered any coverage by their employers or cannot afford their own private health plan.

Since the law's introduction, 7.5 million people have signed up for health insurance.

Republicans have criticised Obama's signature reform as unnecessary government interference in the health system and some sections of American society are unhappy that it has sparked a rise in their insurance policy payments.