Virginia voters have approved a redistricting measure that could hand Democrats control of the thinly-divided US House of Representatives in the midterm elections later this year.

The ballot measure will redraw the state's congressional map to help Democrats flip as many as four House seats held by Republicans.

The state is the latest in a national redistricting arms race that was launched after President Donald Trump urged conservative states to re-examine voting maps to help Republicans keep the party's slim congressional majority.

Control of Congress will be decided in the November midterm elections and each of these newly drawn districts could decide what political party takes the House.

Historically, the party of the current president would lose House seats during this congressional election. If Democrats win in the November race, it will not only serve a blow to Trump's political agenda, but it could open him up to Democratic-led congressional investigations.

In the US, gerrymandering - the redrawing of electoral boundaries to favour a political party - is only illegal if it is based on race.

Democrats in Virginia currently hold six out of the state's 11 seats, and the updated map could allow them to hold up to 10.

"Virginia just changed the trajectory of the 2026 midterms," Democratic state House Speaker Don Scott said on social media.

"At a moment when Trump and his allies are trying to lock in power before voters have a say, Virginians stepped up and leveled the playing field for the entire country," he wrote.

The redistricting referendum is the most expensive ballot measure in Virginia's history by far, according to figures from the Virginia Public Access Project. Over $80m (£59m) was raised as of earlier this month by groups on both sides of the effort.

In his first public comments on Virginia's measure, Trump said on Monday that if House Democrats win a majority in the midterm elections, "it's going to be a disaster".

"I don't know if you know what gerrymandering is, but it's not good," he added.

States usually redraw their voting maps once every decade after new population data is released as part of the US Census.

Texas became the first state to launch a mid-decade change amid pressure from Trump, setting off a race for other states to alter their maps to help their respective political parties.

Texas' new map will give Republicans an advantage in five additional seats.

In response to Trump's support of Texas' changes, California Gov Gavin Newsom launched a campaign last year to suspend the Golden State's independently drawn maps in order to "fight fire with fire".

California voters approved their new maps in a special referendum in November, giving Democrats an edge in five new districts.

Other Republican-led states have changed their maps, too. North Carolina and Missouri also passed new maps that give the party an edge.

Utah has also passed a new map with court-imposed districts that could give Democrats an advantage in one district.