Irish PM: President-elect Biden 'true friend' of Ireland

"I want to congratulate the new President Elect of the USA @JoeBiden," the Irish leader said on Twitter, moments after US networks declared Biden the winner of the bitter White House race over President Donald Trump.

"Joe Biden has been a true friend of this nation throughout his life and I look forward to working with him in the years ahead. I also look forward to welcoming him back home when the circumstances allow!" Martin added.

Joe Biden has won the US presidency over Donald Trump, TV networks projected on Saturday - a victory sealed after the Democrat claimed several key battleground states won by the Republican incumbent in 2016.

CNN, NBC News and CBS News called the race in his favor, after projecting he had won the decisive state of Pennsylvania.

Biden, 77, is the oldest candidate ever elected to the White House. Trump, 74, has made as yet unsubstantiated claims of massive voter fraud, and his campaign has launched legal challenges in several states.

Biden spent eight years as vice president to Barack Obama. His victory comes in his third run for the nation's highest office.