WASHINGTON (AFP) - US lawmakers will vote Thursday (May 4) to repeal and replace Obamacare, Republican House leaders said.

The announcement comes after a new health care reform Bill gained momentum on Wednesday when two key Republican representatives - Fred Upton of Michigan and Billy Long of Missouri - threw their support behind the measure following the addition of US$8 billion to help cover insurance costs for people with pre-existing conditions.

"We will be voting on the health care bill tomorrow. Because we have enough votes," Majority Leader Kevin McCarthy told reporters late Wednesday.

"It'll pass. It's a good bill."

An earlier version of the Republican plan collapsed in March, when opposition from both moderates and conservatives torpedoed their own party's attempt to do away with former president Barack Obama's Affordable Care Act.

President Donald Trump has touted the amended draft multiple times in recent days. Republicans can afford only 22 defectors if the bill is to pass.

Upton, who drafted an amendment to add the US$8 billion, previously opposed the legislation, saying he was uncomfortable with a provision allowing states to remove essential health benefits from patient with pre-existing conditions.

Many health policy experts, however, say US$8 billion will not be enough to help provide coverage for sick people.