Donald trump announced his long-awaited alternative to barack obama's signature healthcare law on thursday, claiming patients would continue to be covered for pre-existing conditions, but without saying how.

The us president said during a speech in charlotte, north carolina that he would sign executive orders to tackle some of the thorniest issues in healthcare policy, including how to provide insurance coverage for previously-known conditions, and how to stop patients getting surprise bills for care outside the scope of their insurance.

Mr trump said he would sign a document to make it the official policy of the government that patients should continue to be covered for all healthcare problems, even without the affordable care act or obamacare, which could be struck down by the supreme court in the coming months. but he did not say how this would make insurers and providers comply.

Experts said the announcement amounted more to an attempt to blunt attacks by his presidential rival joe biden than a serious attempt to introduce a new policy.

Mr trump said: the historic action i am taking today includes the first ever executive order to affirm it is the official policy of the united states government to protect patients with pre-existing conditions.

He added: our opponents the democrats like to constantly talk about and yet people with pre-existing conditions are much safer with us than they are with them. thats signed, sealed and done.

Asked how the government would enforce this however, alex azar, mr trumps health secretary, told reporters: we will work with congress or otherwise to make sure they are protected.

Mr trump said he would also stop patients being billed unexpectedly for treatment they receive that falls outside their insurance plan. mr azar said he would work with congress to create a law to enact that, but that he would take his own regulatory action if congress had not acted by january 1. he did not say what his action would be.

Republicans have long promised to repeal and replace obamacare, although lawmakers have yet to agree on any replacement legislation to make sure tens of millions of people do not lose their insurance coverage.

The trump administration is supporting a legal challenge to the act, which is set to be heard by the us supreme court the week after the presidential election. the death of the liberal supreme court justice ruth bader ginsburg last week could cement a 6-3 conservative majority on the high court, giving the challenge a greater likelihood of success.

Mr biden has sought to use the debate over healthcare to his advantage in recent days, warning that americans coverage is at stake in novembers election. the democratic presidential nominee said this weekend: millions of americans are voting because they know their healthcare hangs in the balance.

Experts said the trump administrations healthcare policy announcement was more campaign rhetoric than a serious effort to rewrite the law.

Brandon barford, a partner at the washington-based consultancy beacon policy advisors, said: it took passing a law to grant those types of consumer protections. if the court strikes that law down, it will take another statute to replace it.