A vote in Congress on Donald Trump’s flagship bill to repeal and replace Obamacare has been postponed until 24 March, amid concerns in the White House over a lack of support from Republicans.

Senior Republican representative Kevin McCarthy said lawmakers would begin debating the bill to roll back Obamacare on Friday, admitting the votes were not yet in place to secure passage.

A White House official confirmed the vote would take place on Friday morning, but did not give an exact time.

The delay comes as around two-dozen Republicans threatened to vote against the bill.

"We're trying very hard to get to yes," Representative Mark Meadows of North Carolina told reporters on Capitol Hill.

He is head of the dissenting faction of House Republicans, the Freedom Caucus. Mr Meadows said his group has seen some "good faith gestures" made by the White House however they still have some concerns.

He said the Freedom Caucus wants "an adequate safety net for people with pre-existing conditions and [that] truly premiums will go down for moms and dads."

They are also worried about how the Republican replacement affects veterans and those with pre-existing conditions, the latter of whom are currently guaranteed coverage under Obamacare.

Faces of Obamacare: The health scheme at the centre of the shutdown Show all 3 1 /3 Faces of Obamacare: The health scheme at the centre of the shutdown Faces of Obamacare: The health scheme at the centre of the shutdown obama.jpg Martin Wolske, 49 and his family, Illinois. His son Eric, 23 (bottom right, dark hair) was recently badly injured in a motorcycle accident. Faces of Obamacare: The health scheme at the centre of the shutdown obama2.jpg Tracy Russo, 31, Washington DC Faces of Obamacare: The health scheme at the centre of the shutdown obama3.jpg Kevin McCollum, 41, and his wife Melissa, 40, Texas

Mr Meadows' group also wants to take out the Obamacare holdover clause on "essential health benefits" which requires insurance companies to provide coverage on a list of items for every beneficiary. Freedom Caucus members say this forces people to pay for coverage they will not need and drives up premiums.

President Trump had promised several times during his campaign to repeal and replace Obamacare, but Mr Meadows does not view the postponement as "a loss" for Mr Trump.