Former US president George W Bush has denounced "bullying and prejudice" in a speech in New York, which appeared to be a sweeping, thinly veiled critique of President Donald Trump.

Key points: Mr Bush spoke of bullying, nativism, and a decline in public confidence in the US

Mr Bush spoke of bullying, nativism, and a decline in public confidence in the US Mr Bush did not mention Mr Trump by name, but attacked some of his principles

Mr Bush did not mention Mr Trump by name, but attacked some of his principles His spokesman said Mr Bush had discussed the issues "for years"

Mr Bush, 71, used the rare public address to discuss nationalism, racial divisions and Russia's intervention in the 2016 election — all flashpoints of his fellow Republican's nine-month White House tenure.

He did not mention Mr Trump by name, but attacked some of the principles that define the 45th president's political brand.

"Bullying and prejudice in our public life sets a national tone, provides permission for cruelty and bigotry, and compromises the moral education of children," Mr Bush said at the Bush Institute's National Forum on Freedom, Free Markets and Security.

"The only way to pass along civic values is to first live up to them."

Mr Trump has used nicknames to demean opponents, such as "Crooked Hillary" for Democrat Hillary Clinton and, more recently, "Liddle" Bob Corker for a Republican senator who dared to challenge him.

Mr Bush, president from 2001-2009, also emphasised the importance of immigration and international trade — two policy areas that Mr Trump has cracked down on while in office.

"We've seen nationalism distorted into nativism, forgotten the dynamism that immigration has always brought to America," he said.

"We see a fading confidence in the value of free markets and international trade, forgetting that conflict, instability, and poverty follow in the wake of protectionism."

Mr Trump alleges Mr Corker "begged" him for endorsement and wanted to be secretary of state. ( Reuters )

Bush maintains speech was not aimed at Trump

Asked whether the speech was aimed at Mr Trump, a spokesman for Mr Bush said the long-planned remarks echoed themes the former president had discussed for years.

"The themes president Bush spoke about today are really the same themes he has spoken about for the last two decades," Bush spokesman Freddy Ford said.

Mr Bush touted US alliances abroad, something Mr Trump has called into question, and denounced white supremacy, which critics have previously accused Mr Trump of failing to do quickly and explicitly this year.

In the speech, Mr Bush described a decline in public confidence in US institutions and a paralysis in the governing class to address pressing needs.

"Discontent deepened and sharpened partisan conflicts. Bigotry seems emboldened. Our politics seems more vulnerable to conspiracy theories and outright fabrication," Mr Bush said.

Mr Trump was a longtime proponent of a false theory that Democratic former President Barack Obama was not born in the United States. Mr Obama, Mr Trump's predecessor, was born in the US state of Hawaii.

Mr Bush said Americans were the heirs of Thomas Jefferson, the third US president, as well as civil rights leader Martin Luther King Jr.

"This means that people of every race, religion, and ethnicity can be fully and equally American," he said.

"It means that bigotry or white supremacy in any form is blasphemy against the American creed."

Mr Bush is the brother of 2016 presidential hopeful Jeb Bush, the former Florida governor nicknamed, belittled and ultimately vanquished by Mr Trump during the race for the Republican nomination.

He joins a slowly growing list of prominent Republicans who have publicly defied Mr Trump, including Republican senator John McCain, who delivered a similar speech this week.

Mr Trump said he had not seen the speech.

AP/Reuters