The US president pledged not speak out over the months-long unrest in the Chinese territory during a phone call with Xi Jinping in which he also discussed his political rivals Joe Biden and Elizabeth Warren, according to CNN.
The report comes after Mr Trump openly urged China to investigate Mr Biden, a Democratic 2020 election frontrunner, and his son Hunter.
“China should start an investigation into the Bidens,” said Mr Trump, unprompted, as he spoke to reporters outside the White House.
The demand came just days after congress launched an impeachment inquiry over allegations the president had pressured Ukraine to probe unsubstantiated corruption claims about the Democrat.
Mr Trump insisted he had not previously asked China to investigate Barack Obama’s vice-president, although he said it was “certainly something we could start thinking about”.
But CNN, citing two unnamed sources, reported that Mr Trump previously brought up Mr Biden during an 18 June phone call with Mr Xi.
He also reportedly raised the subject of Ms Warren, another Democratic presidential hopeful, who was climbing in the polls at the time.
The sources did not give details of the content of the discussions, but said the White House record of the call was later stored in the same high-security electronic database used to house the now-infamous phone conversation between Mr Trump and Ukrainian president Volodymyr Zelensky.
Ms Warren called for a transcript of the call between the American and Chinese leaders to be made public.
“Trump can say what he wants about me, but it’s outrageous that any president would sell out the people of Hong Kong behind closed doors,” she tweeted.
Earlier this week Mr Trump faced criticism for tweeting congratulations to Mr Xi for 70 years of Communist Party rule in China, while remaining quiet on the violent crackdown on protesters in Hong Kong.
His call for China to investigate Mr Biden came ahead of high-stakes trade talks in Washington next week.
The president doubled down on his comments on Twitter, insisting he had an “absolute right, perhaps even a duty, to investigate” corruption and “that would include asking, or suggesting, other countries to help us out”.
Mr Trump has accused Hunter Biden of using his father’s influence to secure China’s financial backing for his investments, but he has offered no evidence of any wrongdoing.
Mr Biden’s campaign team said the president was ”desperately clutching for conspiracy theories that have been debunked and dismissed by independent, credible news organisations” to distract from impeachment proceedings and bolster his bid for a second term in the White House.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies