WASHINGTON (REUTERS) - Democrats picked up seats in Colorado and Arizona, and Republicans picked one up in Alabama in the battle for control of the US Senate in Tuesday's (Nov 3) elections. In Georgia, a Republican-held seat was now headed to a January run-off.

Elsewhere, Republicans held off Democratic challengers in five of the 14 most competitive races, bolstering their chances that they would retain a majority in the 100-seat chamber. The final outcome may not be clear for some time.

Republicans currently hold 53 seats. Democrats need to win four seats to take a majority, or three if Joe Biden wins the White House, which would give a Vice-President Kamala Harris the tie-breaking vote.

A Democratic victory could lead to a new era in US politics, if the party also captures the White House and holds onto the US House of Representatives.

Here are the results so far, based on projections by television networks and Edison Research:

Arizona: Democratic former astronaut Mark Kelly topped Republican Senator Martha McSally after holding a wide fundraising lead. Ms McSally, a former US representative and US Air Force combat pilot, was appointed to the seat once held by the late Republican Senator John McCain after losing her 2018 Senate bid to Democrat Kyrsten Sinema.

Montana: Republican Senator Steve Daines held off a challenge from two-term Governor Steve Bullock, a former presidential candidate who branded himself as an independent-minded Democrat. Mr Daines, a former congressman and software executive, is known as a reliable conservative and has touted his ties to Trump.

Iowa: Republican Senator Joni Ernst defeated Democratic challenger Theresa Greenfield. Ms Ernst used her role in US Supreme Court Justice Amy Coney Barrett's confirmation to appeal to conservative-leaning voters. Greenfield, an urban planner and real estate developer, accused Ernst of being a rubber stamp for President Donald Trump and not taking the Covid-19 pandemic seriously enough.

Georgia: Republican Senator Kelly Loeffler and Democrat Raphael Warnock were headed to a Jan 5 run-off election after neither secured a majority in a multi-party, multi-candidate "jungle primary" special election. The unusual race was prompted by the retirement of Republican Senator Johnny Isakson. Ms Loeffler was appointed last year to fill his seat. The contest featured 21 candidates in all, including another prominent Republican, Representative Doug Collins.

Kansas: Republican Representative Roger Marshall defeated Democratic state Senator Barbara Bollier in a surprisingly competitive race. Democrats haven't won a Senate seat in Kansas, one of the country's most reliably Republican states, since 1932. But Ms Bollier mounted a strong challenge in the race for the seat of Republican Senator Pat Roberts, who is retiring.

Alabama: Republican Tommy Tuberville, a former Auburn University football coach, defeated incumbent Democratic Senator Doug Jones. Mr Jones had been considered the most vulnerable Democrat in the Senate. He won the seat in an upset in 2017 after Republican Jeff Sessions vacated it to become Mr Trump's attorney-general. Mr Tuberville, a popular figure in football-mad Alabama, defeated Mr Sessions' attempted comeback earlier this year.

Colorado: Democratic challenger John Hickenlooper defeated incumbent Republican Senator Cory Gardner. Mr Gardner, a former US representative who entered the Senate in 2015, was among the most vulnerable Senate Republicans partly because of his allegiance to Mr Trump in a state that has gone Democratic in the last three presidential elections. Mr Hickenlooper is a former two-term governor and 2020 presidential hopeful. He raised far more money than Mr Gardner and consistently led in opinion polls.

South Carolina: Senator Lindsey Graham, one of Mr Trump's closest allies in Congress, held off a surprisingly strong challenge from Democrat Jaime Harrison, who raised staggering amounts of money. Mr Graham was last re-elected to the Senate in 2014 with more than 55 per cent of the vote in the deeply Republican state. This year, he faced scepticism from conservative voters who doubted the sincerity of his support for Mr Trump, analysts say, while moderates were disappointed by his loyalist stance.

Texas: Veteran Republican Senator John Cornyn held off a challenge from Democrat M.J. Hegar. Texas, once a Republican stronghold, has grown increasingly competitive in recent years as the population has grown more diverse and Mr Trump's polarising presidency has alienated suburban women. The state became a surprise battleground in this year's presidential race, where opinion polls have shown Mr Trump narrowly leading Mr Biden. Mr Cornyn, who has been in the Senate since 2002, was projected to win re-election shortly after polls closed.

Here are other races that are likely to determine which party will control the Senate:

Republican-held seats

Alaska: Freshman Republican Senator Dan Sullivan is favoured to hold on to his seat in a closely contested election battle against Mr Al Gross, an independent who is running as the Democratic Party nominee.

Georgia: First-term Republican Senator David Perdue, a wealthy businessman who promotes himself as a Trump ally, faces Democratic challenger Jon Ossoff, an investigative journalist and media executive. The seat is one of two in Georgia that could be settled by a January runoff if no candidate receives more than 50 per cent of the vote.

Maine: Four-term Republican Senator Susan Collins, a New England moderate long known for her independence, faces Maine House of Representatives Speaker Sara Gideon. Voters' second choices could be taken into account under Maine's unique runoff system if no candidate has more than 50 per cent of the vote.

North Carolina: North Carolina has erupted into one of the most dramatic Senate races in the country, with Democrat Cal Cunningham's candidacy tripped up by a sex scandal after he had dominated the campaign for months. The Republican incumbent, Mr Thom Tillis, declared victory, though the race had not yet been called.

Democratic-held seats

Michigan: Democratic Senator Gary Peters has been favored to hold onto his seat against Republican challenger John James in a state that represents a major battleground for Trump's re-election bid.

For live updates and results, follow our US election live coverage.