Media playback is unsupported on your device Media caption John McCain returned to the Senate to applause

The US Senate has rejected a Republican plan to replace President Barack Obama's signature healthcare policy.

The 57-43 vote defeat marks the start of a days-long debate on a sweeping overhaul that critics fear could deny healthcare to millions of Americans.

The Better Care Reconciliation Act (BRCA) was crafted over two months but attention now turns to other options.

President Donald Trump has urged senators to pass a bill, without indicating which one he supports.

A repeal-only bill, which would consign so-called Obamacare to history in two years, to give time to Republicans to devise a replacement, could be debated and voted on next.

But that measure - which non-partisan analysts say will take health insurance from more than 30 million people - has already failed to win enough support in the Republican party.

Other attempts to replace Obamacare have collapsed in recent weeks due to divisions in the party.

President Trump had made scrapping the policy a key campaign pledge. He says the system is "torturing" Americans.

He secured a victory on Tuesday when the Senate agreed to allow the debate on health care legislation reform to go forward, but only after Republican Vice-President Mike Pence cast the tie-breaking vote in support of the bill.

Senator John McCain, who was recently diagnosed with an aggressive brain tumour, received a standing ovation as he returned to Congress to cast his "Yes" vote.

President Trump tweeted his thanks to the Arizona senator for playing "such a vital role" in the vote.

But in an early morning tweet on Wednesday, Mr Trump lambasted Senator Lisa Murkowski of Alaska for opposing the Republican plan.

What bills could come forward?

The key repeal-and-replace bill, the BCRA, has fallen by the wayside.

Next could be a repeal-only bill with a two-year delay, in the hope of finding agreement before that time elapses.

But senators will also consider a "skinny bill", a far narrower measure that would scale back some of the more controversial elements in an effort to get a wider consensus.

A special Senate-House of Representatives committee would then be tasked with finalising a bill that could still see changes during negotiations.

If successful, the full House and Senate would again have to approve the measure.

US Health and Human Services Secretary Tom Price told CNBC on Wednesday that Senate Republicans should aim for the "lowest common denominator" to secure the 50 votes need to pass a bill.

What have Republicans proposed?

Republicans have long railed against Obamacare as government overreach, criticising the system for introducing government-run marketplaces, where premiums have risen sharply for some people.

The party's proposed alternative includes steep cuts to Medicaid, a healthcare programme for the poor and disabled.

Image copyright Reuters Image caption Mitch McConnell said senators had "a duty to act"

And it removes Obamacare's individual mandate requiring all Americans to have health insurance or pay a tax penalty.

About 20 million people gained health insurance under former President Obama's Affordable Care Act.

The non-partisan Congressional Budgetary Office (CBO) found the bill would strip 22 million Americans of health insurance over the next decade.

If Republican senators elect to repeal key provisions of the law without immediately replacing it, the CBO estimates about 32 million consumers would lose insurance over the next 10 years.

Six months of Trump