Ghana's President Nana Akufo-Addo on Saturday said Donald Trump's reported description of African nations as "shithole countries" was unacceptable, while his predecessor branded the US head of state a racist.

President Akufo-Addo tweeted that Trump's reported language was "extremely unfortunate", adding: "We are certainly not 'a shithole country'.""We will not accept such insults, even from a leader of a friendly country, no matter how powerful."

Ghana is widely seen as a stable, peaceful country in an often turbulent region, and has close ties to the United States.

In 2009 Trump's predecessor, Barack Obama, chose Ghana's capital Accra to set out his foreign policy goals for Africa in a speech in which he said he saw Africa "as a fundamental part of our interconnected world".

Africans were "partners with America on behalf of the future we want for all of our children. That partnership must be grounded in mutual responsibility and mutual respect", he said.

Akufo-Addo's comments follow a strongly worded African Union statement on Friday and a demand from African ambassadors at the United Nations for a retraction and an apology.

The group of UN diplomats said it was "extremely appalled at, and strongly condemns the outrageous, racist and xenophobic remarks".

Ghana's former president John Dramani Mahama, whom Akufo-Addo defeated in elections just a month after Trump's own win at the polls, on Twitter asked: "Isn't Trump demonstrating that he's nothing but a racist and pursuing a policy of 'Make America White Again'?"

He also highlighted the contrast between Trump's praise for Africa last year when he met leaders from the continent on the sidelines of the UN General Assembly.

"Shithole? Thought they said he was so impressed with us just last September?" Mahama tweeted under a mocked-up photograph of Trump being shown a map of Africa in which all the countries were labelled "Nambia".

Trump was widely derided last year after twice referring to Namibia as "Nambia" at the September meeting.

Namibia on Saturday added its voice to the chorus of complaints, saying the president's language had "no place in diplomatic discourse" and was "contrary to the norms of civility and human progress".

"The Africa we know and live in is one that is recovering economically and rising," it added.

"The USA we know is one that was built with blood and sweat of African slaves and immigrants from all over."

Trump reportedly demanded to know why the US should accept immigrants from "shithole countries", after lawmakers raised the issue of protections for immigrants from African nations, Haiti and El Salvador.

He has since denied using the reported language.