Donald Trump has said he wants Ukraine and China to investigate political rival and former Vice President Joe Biden and his son – openly advocating an action that triggered a Democratic impeachment inquiry in Congress.

Speaking to reporters on Thursday, the US president was asked what he wanted Ukrainian President Volodymyr Zelenskiy to do after a whistleblower complaint exposed his efforts to have the country launch an investigation into Biden and his son, Hunter.

“I would recommend that they start an investigation into the Bidens,” Trump said.

Trump also said he believed China should launch a probe of the Bidens, alluding to unproven allegations he and his lawyer have made about Hunter Biden’s business dealings in China.

The president said: “And by the way, likewise, China should start an investigation into the Bidens. Because what happened in China is just about as bad as what happened with Ukraine.”

Trump is the target of an impeachment investigation after making such a request to Ukraine.

Trump said he had not directly asked Chinese President Xi Jinping to investigate Biden and his son – but said it’s “certainly something we could start thinking about”.

Trump and personal lawyer Rudy Giuliani have also tried to raise suspicions about Hunter Biden’s business dealings in China, leaning on the writings of conservative author Peter Schweizer.

But there is no evidence that the former vice president benefited financially from his son’s business relationships.

Trump’s requests for Zelenskiy to dig up dirt on Biden, as well as Giuliani’s conduct, are at the centre of an intelligence community whistleblower complaint that sparked the Democratic impeachment probe in Congress last week.

Hunter Biden served on the board of a Ukrainian petrol company at the same time his father was leading the Obama administration’s diplomatic dealings with Kiev.

Though the timing raised concerns among anti-corruption advocates, there has been no evidence of wrongdoing by either the former vice president or his son.

Biden is currently one of the pacesetters in the Democratic party primaries that will determine Trump’s opponent in next year’s presidential election.