Donald Trump's wife, Melania, took centre stage on the first day of the Republican National Convention, but found herself in the midst of an embarrassing plagiarism controversy.

The billionaire businessman's wife appeared to have taken liberal inspiration from a 2008 speech by US First Lady Michelle Obama for her own address to the Republican convention on Monday night.

A Trump campaign official suggested the similarity to Obama's speech may have been the result of an error by her team of speech writers.

However, before her speech, Mrs Trump, a Slovenian-born jewelry designer and former model, told NBC's Matt Lauer: "I wrote it ... with as little help as possible."

A spokesman for the Trump campaign called the speech a success, but suggested her writers may have mistakenly injected some borrowed language.

"In writing her beautiful speech, Melania's team of writers took notes on her life's inspirations, and in some instances included fragments that reflected her own thinking," Jason Miller, Trump's senior communications adviser, said in a statement.

The fragments in question included the following:

"My parents impressed on me the values that you work hard for what you want in life; that your word is your bond and you do what you say and keep your promise; that you treat people with respect," Mrs Trump told the convention in Cleveland.

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In her 2008 speech, Obama said: "And Barack and I were raised with so many of the same values: that you work hard for what you want in life; that your word is your bond and you do what you say you're going to do; that you treat people with dignity and respect."

Also in her speech, Mrs Trump said: "And we need to pass those lessons on to the many generations to follow, because we want our children in this nation to know that the only limit to your achievements is the strength of your dreams and your willingness to work for them."

And in 2008, Obama said: "Because we want our children, and all children in this nation, to know that the only limit to the height of your achievement is the reach of your dreams and your willingness to work for them."

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'Kind and fair'

Mrs Trump's speech was the highlight of a chaotic opening day at the Republican convention that is set to formally nominate her husband as the party's presidential candidate later this week.

"The row over the speech will drown out everything else, including the split in the party," said Al Jazeera's Alan Fisher, who was at the convention in Cleveland.

"For a convention that was meant to be about competence and unity, it's off to a very bad start," he said.

A beaming Trump personally introduced his wife to delegates gathered in Cleveland, which was a break with tradition to appear before his actual nomination.

Mrs Trump used the occasion to take some of the rough edges off her combative husband, who has roiled the campaign trail with inflammatory attacks on Muslims, Mexicans and his many political rivals.

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"He's tough when he has to be, but he's also kind and fair and caring," Mrs Trump said, describing her husband as "intensely loyal" to family, friends, employees and the country.

"If you want someone to fight for you and your country, I can assure you, he's the guy," she said.

Anti-Trump delegates at the convention walked out in protests after a vote to oppose his candidacy failed.

Some of the biggest Republican names - the Bush family and John McCain - were also absent from the convention while on the streets of Cleveland, protesters marched against Trump's bigotry and xenophobia.