US president-elect Donald Trump is sending shockwaves through the domestic and international front with his latest nominations for key political posts.

On the domestic front, he has named firebrand ex-lawmaker Matt Gaetz as his pick for attorney general, choosing a fierce defender who would be well placed to make good on the his threats of revenge against political foes.

Gaetz is among Trump's most controversial nominations as he looks to fill his cabinet after victory against Democrat Kamala Harris in last week's presidential election.

Gaetz quit his seat in the House hours after Trump's bombshell announcement on Wednesday.

Democrats fear Gaetz, 42, will help Trump weaponize the department to launch exactly those types of "show trial" prosecutions.

As attorney general, Gaetz would drive all aspects of the work of the department, which for years has carried out an investigation into sex trafficking and obstruction of justice allegations involving him.

House Republicans were meeting behind closed doors when news of Gaetz's nomination emerged - prompting "an audible gasp."

Alaska senator Lisa Murkowski said: "Do you think he's a serious candidate? Not as far as I'm concerned." Her colleague, Susan Collins, said she was "shocked."

Trump tapped Tulsi Gabbard as director of national intelligence. The former Democratic congresswoman has little direct experience in intelligence and had not been widely expected to be tapped for a job that oversees 18 spy agencies.

Most consequently for Beijing, Trump's nomination of China hardliner Marco Rubio for secretary of state signaled he could go beyond his focus on tariffs and trade to a more hawkish stance towards China as the US' top strategic rival.

Rubio's selection came along with other cabinet picks that might upset China, such as Representative Mike Waltz as national security adviser and John Ratcliffe to lead the Central Intelligence Agency.

Taken together, they suggest Trump wants to upend the Biden administration's approach of "managing competition" with Beijing on issues such as Taiwan and China's role in the US fentanyl crisis.

Rubio "believes in his heart that China is an enemy of the United States," said David Firestein, an ex-US diplomatic expert on China, adding that Rubio's belief in existential zero-sum competition with China would "raise the decibel level" of US-China relations.

His selection will put a China antagonist with significant foreign policy experience at the center of cabinet debates.

Trump has pledged to end China's most-favored-nation trading status and slap tariffs on Chinese imports in excess of 60 percent - much higher than those imposed during his first term.

The staunchly anti-communist Cuban-American's support for Hong Kong democracy protesters earned him Chinese sanctions in 2020.

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Trump's picks send threatening hints home and abroad