One week after the 2018 US midterm election day, the Democratic party have flipped another Republican held senate seat, as Democrat Kyrsten Sinema have been declared winner of the Arizona Senate race, the first for the democratic party in 30 years.

The seat currently held by Republican Jeff Flake -who is retiring from congress- bring the number of Democratic seat in the Senate to 47, though the Republican still have a majority with at 51 seats.

42-year-old Sinema, a U.S. representative and former social worker, spoke to supporters on Monday night after the result was declared in her favour, saying: "It won't be easy and it won't happen overnight, but we can work together to meet the challenges our country faces."

"We can do this differently. For our future, for Senator McCain and for each other, I think we must."

Her Republican opponent Martha McSally, conceded the election and congratulated Sinema.

"I wish her all success as she represents Arizona in the Senate," McSally, with her pet dog beside her, said in a video she posted to social media.