US President Donald Trump has moved a step closer to scrapping his predecessor's signature healthcare law, after US lawmakers backed a bill to repeal and replace it.

The legislation was narrowly passed in the House of Representatives after intense lobbying from supporters and opponents of the Affordable Care Act - known as Obamacare.

The president insists the new plan means people's insurance premiums will fall – however it still has to get through the Senate where it is likely to face stiff opposition.

Opposition politicians, including minority house leader Nancy Pelosi, have attacked those who voted the repeal through the House:

“When you know the facts and care about people, you can’t possibly vote for the bill that they voted for,” said Ms Pelosi. “So what did they do? Either they don’t know or they don’t care.”

The vote is a major victory for President Trump - who made dismantling the healthcare reform package one of his key election pledges - but failed in his first attempt to push his alternative through Congress.

Speaking in the White House Rose Garden surrounded by many of the Republicans who passed the bill, the President promised to "finish off" Obamacare - which he has branded a "catastrophe."

"It's dead, it's essentially dead," he added.

The Republican replacement for Obamacare - the American Health Care Act - could see some 24 million Americans stripped of their health insurance, according to estimates.

Shortly after the bill was passed by 217 votes to 213, jubilant Republican House Speaker Paul Ryan tweeted: "This is a victory for conservatism.”

"We are continuing to uphold our promises to the American people by fixing our broken health care system."

As Republicans crossed over the vote threshold to pass the bill, Democrats in the House began singing "Na na, na na na na, hey hey hey, goodbye," a reference to their belief Republicans will lose in the 2018 midterm elections as a result.

Obamacare - which was passed in 2010 and saw 20 million previously uninsured Americans gain coverage - had been gaining support in opinion polls.

But Republicans fought a seven-year battle to overturn it - claiming it as an example of government overreach that drove up healthcare costs for millions of people.

The American Health Care Act aims to repeal most Obamacare taxes, including a penalty for not buying health insurance.

It would also slash funding for Medicaid, the programme that provides insurance for the poor, and roll back much of Medicaid's expansion.

One of the central issues in the House debate was the treatment of people with "pre-existing" conditions.

Obamacare prevented insurers from charging those with pre-existing conditions higher rates, a common practice before its implementation.

It also required them to cover 10 essential health benefits such as maternity care and prescription drugs.

The Republican bill passed on Thursday would allow states to opt out of those provisions.

While insurers could not deny people insurance because of pre-existing conditions, they would be allowed to charge them as much as they want.

Additional reporting from IRN ...