US-China ties have grown increasingly strained in recent years under the administration of incumbent Donald Trump, and relations are as icy as at any time since formal ties were established four decades ago.

"We respect the choice of the American people. We express our congratulations to Mr Biden and Ms Harris," said foreign ministry spokesman Wang Wenbin at a regular press briefing, referring to incoming vice president Kamala Harris.

Wang said China understands "the result of the US election will be determined in accordance with US laws and procedures".

China was previously among a handful of major countries including Russia and Mexico that had not congratulated the president-elect, with Beijing commenting earlier this week simply that it had "noticed Mr Biden declared he is the winner".

Since US media called the presidential race, Trump has not conceded to Biden as is traditional practice once a winner is projected.

Trump's four years in the White House have been marked by a costly trade war between the two powers, with Beijing and Washington also sparring over blame for the Covid-19 pandemic and China's human rights record in Xinjiang and Hong Kong.

Under his "America First" banner, Trump has portrayed China as the greatest threat to the United States and global democracy.

CNN reports for just the second time in more than seven decades, a Democrat will carry Arizona in a presidential election, a monumental shift for a state that was once a Republican stronghold.

CNN projected on Thursday that President-elect Joe Biden will carry Arizona, defeating President Donald Trump and providing Democrats in Arizona and the universe of allied grassroots organizations in the state with a crowning achievement a decade in the making.

Biden's win of Arizona's 11 electoral votes brings his total to 290 while Trump has won 217 electoral votes.

Jacaranda FM/AFP