Donald Trump’s administration has conceded the Republican healthcare bill must change if it has any hopes of being passed through Congress.

House speaker Paul Ryan said “some necessary improvements and refinements” to the legislation will be made, just days after a report found the Obamacare replacement would leave millions without health cover.

The legislation cleared its first hurdle after receiving approval from the Budget Committee, in spite of the damning report and numerous defections from Republican representatives.

David Brat, Gary Palmer and Mark Sanford joined the panel's Democrats in voting against the bill, as the White House and Republican leaders discussed changes to satisfy conservatives who oppose it.

"I don't think we are anywhere near passage," Mr Brat said after the vote, noting that Republican conservatives as well as moderates had problems with the bill.

However Mr Ryan said: "We are on track and on schedule."

Even if it passes the House, it faces an uphill battle in the Senate, where Republicans hold a slimmer majority.

The bill faces unified Democratic opposition, as well as criticism from leading healthcare providers, including doctors and hospitals.

Independent analysis by the Congressional Budget Office (CBO), similar to Britain’s Office for Budget Responsibility, estimated that 14 million more people would be uninsured next year under the legislation than under under the current arrangement – a figure expected to rise to 24 million by 2026.

Mr Trump told a Nashville, Tennessee rally on Wednesday: “It’s going to be great.”

Democrats say the Republican plan could hurt the elderly, poor and working families while giving tax cuts for the rich. Senate Minority Leader Chuck Schumer called it "a wreck".

"It's vintage Donald Trump: talks like a populist, but when he acts, it's hard-right, favouring the special interests and hurting the middle class and those trying to get there," Mr Schumer said.

However, White House budget chief Mick Mulvaney said “there's no perfect piece of legislation.”

“There's gonna be this framework that's gonna be added to or subtracted to during the process, and eventually it's going to pass the House and it's going to pass the Senate," he told Fox News.