Republicans will hold a narrow majority in the US House of Representatives next year, after Democrats won the final uncalled race in California on Tuesday.

A slender win for Democratic candidate Adam Gray in California's 13th congressional district leaves his party on 215 seats in the lower chamber of Congress, compared with the Republicans' 220.

The trifecta of House, Senate and presidency - last achieved at the start of Donald Trump's first term in 2017 - will give the president-elect significant power to enact his agenda on the economy, immigration and other key issues.

But with a narrow House majority Republicans could still struggle to secure enough votes for some actions.

A majority is achieved in the 435-seat chamber when a party wins 218 seats - which the Republicans surpassed.

The final congressional race to be called in the country was in California's Central Valley - nearly a month after America went to the polls on 5 November. It is not unusual for some contests to take days or weeks to be called.

The race ended in victory for Gray over the Republican incumbent John Duarte, by a margin of fewer than 200 votes, according to the BBC's US partner CBS News.

Gray said it showed the area was "ready for independent and accountable leadership that always puts the Valley's people ahead of partisan politics".

In the presidential contest, Trump beat Kamala Harris in all seven closely watched swing states - handing him a decisive advantage as he mounted a comeback unmatched by any previously defeated president in modern times.