Democrats have won a majority in the US House of Representatives, gaining the power to investigate President Donald Trump and help shape America's political agenda for the next two years.

The party picked up at least two dozen House seats in the American midterm elections, capturing the 218 needed to break the Republicans' eight-year hold on the legislature that began with the Tea Party revolt of 2010.

While Republicans retained control of the US Senate, the Democratic win in the House ends the Republican monopoly on power in Washington and opens a new era of divided government.

Democratic candidates flipped seats in a host of suburban districts outside Washington, New York, Philadelphia, Miami, Chicago and Denver, including many that were won by Hillary Clinton in the 2016 presidential poll.

Democrats also made inroads in Trump country, winning several races dominated by white working-class voters.

As the majority party, the Democrats will chair powerful committees and have subpoena power to seek Mr Trump's tax returns and more aggressively investigate Russian interference in the 2016 election, as well as possible collusion by the Trump campaign.

Democratic leader Nancy Pelosi called it a "new day in America".

The campaign unfolded against a backdrop of ugly rhetoric and angry debates on immigration, healthcare and the role of US Congress in overseeing the president.

Midterm elections are typically difficult for the party in power, but the Republicans' hold on power was further weakened by an unusually large number of retirements as well as infighting between conservatives and centrists over their allegiance to Mr Trump.

The Democrats, in turn, benefited from extraordinary voter enthusiasm, robust fundraising and unusually fresh candidates. More women than ever were running, along with veterans and minorities - many of them motivated by revulsion over Mr Trump's presidency.

As the results came in, voters were on track to send at least 99 women to the House, shattering the previous record of 84.

In trying to stem Republican losses, Donald Trump made only passing reference to his 1.5 trillion-dollar (£1.14 trillion) tax cut - the Republican-controlled Congress' signature achievement - and instead barnstormed through mostly white regions of the country, interjecting dark warnings.

He predicted an "invasion" from the migrant caravan making its way through Mexico towards the US and decried the "radical" agenda of speaker-in-waiting Ms Pelosi.

Mr Trump also took little responsibility for the House, saying his focus was on saving the Senate.

On Tuesday night, he called to congratulate Ms Pelosi and acknowledged her plea for bipartisanship.

Healthcare and immigration were high on voters' minds as they cast ballots, according to a ranging survey of the American electorate conducted by The Associated Press. AP VoteCast also showed a majority of voters considered Mr Trump a factor in their votes.

In the Miami area, former Clinton administration cabinet member Donna Shalala won an open seat, while Republican congressman Carlos Curbelo lost his bid for a third term in another district.

In the suburbs outside the nation's capital, Virginia representative Barbara Comstock - branded Barbara "Trumpstock" by Democrats - lost to Jennifer Wexton, a prosecutor and state legislator.

Outside Richmond, Virginia, one-time Tea Party favourite Dave Brat lost to Democrat Abigail Spanberger, a former CIA operative motivated to run for office after the Republican vote to gut the Affordable Care Act.

Pennsylvania was particularly daunting for Republicans after court-imposed redistricting and a rash of retirements put several seats in play.

Democratic favourite Conor Lamb, who stunned Washington by winning a special election in the state, beat Republican Keith Rothfus in a new district. At least three other red districts flipped to blue.

In Kansas, Democrat Sharice Davids beat a Republican incumbent to become one of two Native American women - alongside Deb Haaland of New Mexico - elected to the House. Ms Davids is also openly gay.

Democrats welcomed other firsts, including two Muslim-American women, Rhasida Tlaib of Michigan and Minnesota's Ilhan Oman, who is also the first Somali-American elected to US Congress. The Republican side of the aisle elected mostly white men.

In Kentucky, one of the top Democratic recruits, retired Marine fighter pilot Amy McGrath, lost her bid to oust to three-term representative Andy Barr in the Lexington-area district.

Republicans had expected the party's tax plan would be the cornerstone of their election agenda this year, but it became a potential liability in key states along the east and west coasts where residents could face higher tax bills because of limits on property and sales tax deductions.