A handful of renegade Republicans in the US House of Representatives have joined all Democrats to pass a bill that would extend healthcare subsidies for millions of Americans.

Seventeen moderate Republicans defied party leadership to help approve the measure by 230-196. But the legislation could face an uphill battle in the Senate.

House Speaker Mike Johnson had opposed a renewal of the pandemic-era tax credits, arguing they are rife with fraud, but some of his rank-and-file crossed the aisle to force a vote.

Insurance premiums through the Affordable Care Act (ACA), also known as Obamacare, have more than doubled for some 20 million Americans since the subsidies expired at the end of last year.

The measure passed on Thursday would extend the Covid-era subsidies for another three years.

Centrist Republicans have said they would rather support some kind of extension than do nothing at all.

About 24 million Americans buy health insurance through the ACA marketplace, and the majority were used to receiving tax credits to lower the monthly price.

Those tax credits, also referred to as subsidies, were first introduced through former President Barack Obama's ACA in 2014. They were then expanded during Covid.

The bill's passage is a setback for House Republican leadership, which controls the lower chamber of Congress by a narrow majority.

The vote was forced when four members of the Republican rank-and-file defected last month to support a procedural tactic known as a discharge petition.

The House measure does not have to be brought up in the Senate, which has already rejected it.

Even if the legislation was brought back to the upper chamber of Congress, it does not currently have the 60 votes it needs to pass.

Senators have said they are working on their own bipartisan compromise, the text of which should be available next week.

Though the House vote was largely symbolic, it places lawmakers on the record ahead of this November's midterm elections, when healthcare and affordability are likely to be hot campaign issues.