Republicans have struck blows against the Democrats in the race to control Congress, flipping Senate seats in West Virginia and Ohio.

Jim Justice, West Virginia's current governor, is projected to win the seat vacated by the former Democrat Joe Manchin, while Bernie Moreno in Ohio unseated Democratic incumbent Sherrod Brown.

The projected results would move the Senate to a 51-49 split in favour of the Republicans. Results in other seats are pending, however.

The party also currently holds a majority in the House of Representatives. Winning the Senate would give it greater leverage to enact its agenda.

Republican control of the House, Senate and the White House would give it broad power to pass laws and enact the president's partisan agenda.

In Ohio, Brown was projected to lose to Moreno, a Colombian immigrant and former car sales magnate who portrayed the veteran politician as "too liberal for Ohio".

The contest has been called the most expensive Senate race in US history.

Brown told supporters that the result was a "disappointment but not a failure", adding: "I'm not giving up on our fight for workers and I know you won't either".

The seat in West Virginia is projected to flip Republican. It was contested after the retirement of Manchin, who frequently clashed with members of his own party before turning independent.

Justice had himself been a Democrat before switching parties to Republican at a Trump rally in 2017.

A total of 34 Senate seats are being contested on Tuesday. Republicans were projected to retain control of seats throughout the country.

In Texas, Trump ally Ted Cruz fended off a robust challenge from former NFL player Colin Allred to win a third term.

Democrats had launched a concerted effort to beat Cruz but the party has not won a state-wide election in the state for more than 30 years.

Rick Scott, a Republican incumbent in Florida, was projected to retain his seat despite a challenge by former Miami-area Congresswoman Debbie Mucarsel-Powell, a Democrat who migrated from Ecuador as a child.

Speaking at a victory rally, Scott predicted that Republicans would seize the majority in the Senate and that he would be selected as Senate Majority Leader.

"Florida is the centre of the Republican party of this country," he told the crowd. "Washington can learn a hell of a lot from what we've done right here in this great state."

Democrats held a seat in Delaware, a state that President Joe Biden represented as a senator for 36 years, with a victory for fourth-term Congresswoman Lisa Blunt Rochester.

In Maryland, the Democrats retained a seat vacated by Ben Cardin, with Angela Alsobrooks beating the popular Republican Governor Larry Hogan.

They will become the first black female senators to represent their respective states.

In New Jersey, Democrats retained a seat that was vacated by Bob Menendez, who resigned after he was found guilty of accepting bribes for political favours. Andy Kim, 42, will become the first ever Korean-American senator.

Other contests that would swing control of the upper chamber are taking place in Arizona, Pennsylvania, Montana, Michigan, Nevada, Nebraska and Wisconsin.

Both parties are also vying for control of the House, although the balance of power there will not be known for several days.

The vast majority of House elections are happening in "safe districts" - regions where one party is nearly certain to win. But a handful of other races in swing districts could determine who controls Washington DC.

House races that could swing the balance are taking place a wide variety of states, with closely watched elections happening in California, New York, Washington, Maine and Alaska.