Hillary Clinton has cast herself as a unifier for divided times, an experienced leader steeled for a volatile world - and aggressively challenged Donald Trump's ability to do the same.

"Imagine him in the Oval Office facing a real crisis," the former US secretary of state and first lady said, as she accepted the Democratic nomination for president early on Friday.

"A man you can bait with a tweet is not a man we can trust with nuclear weapons."

Mrs Clinton took the stage to roaring applause from flag-waving delegates on the final night of the Democratic convention in Philadelphia, relishing her nomination as the first woman to lead a major US political party.

But her real audience was the millions of voters watching at home, many of whom may welcome her experience, but question her character.

She acknowledged those concerns briefly, saying: "I get it that some people just don't know what to make of me." But her primary focus was persuading Americans to not be seduced by Republican presidential candadate Mr Trump's vague promises to restore economic security and fend off threats from abroad.

Mrs Clinton said the US needed a leader who would work with allies to keep America safe.

The presidential election presented a stark choice on national security, she said, with the US facing "determined enemies that must be defeated".

She said people wanted "steady leadership", vowing to stand by Nato allies against any Russian threats.

And she pledged to defeat the Islamic State group with air strikes and support for local ground forces, while authorising a "surge" in intelligence to prevent terrorist attacks.

"We will prevail," she said.

She also said she was proud of the Iran nuclear and global climate agreements and both must be enforced now. Neither deal happened while she was in government.

Mrs Clinton's four-day convention began with efforts to shore up liberals who backed Bernie Sanders in the Democratic primary and it ended with an outstretched hand to Republicans and independents unnerved by brash billionaire Mr Trump.

A parade of military leaders, law enforcement officials and Republicans took the stage ahead of Mrs Clinton to endorse her in the general election contest.

"This is the moment, this is the opportunity for our future," said retired Marine general John Allen, a former commander in Afghanistan. "We must seize this moment to elect Hillary Clinton as president of the United States of America."

American flags waved in the stands of the packed convention hall. There were persistent, but scattered calls of "No more war", but the crowd drowned them out with chants of "Hill-a-ry" and "U-S-A!"

Mrs Clinton now has just over three months to persuade Americans that Mr Trump is unfit for the Oval Office and overcome the visceral connection he has with some voters in a way the Democratic nominee does not.

She embraced her reputation as a studious wonk, a politician more comfortable with policy proposals than rhetorical flourishes. "I sweat the details of policy," she admitted.

Mrs Clinton's proposals are an extension of President Barack Obama's two terms in office: tackling climate change, overhauling the nation's fractured immigration laws and restricting access to guns.

She disputed Mr Trump's assertion that she wanted to repeal the Second Amendment, saying: "I'm not here to take away your guns. I just don't want you to be shot by someone who shouldn't have a gun in the first place."

Campaigning in Iowa Thursday, Mr Trump said there were "a lot of lies being told" at Mrs Clinton's convention. In an earlier statement, he accused Democrats of living in a "fantasy world", ignoring economic and security troubles as well as Mrs Clinton's controversial email use at the US State Department.

The FBI's investigation into her use of a private internet server did not result in criminal charges, but it did appear to deepen voters' concerns with her honesty and trustworthiness.

A separate pre-convention controversy over hacked Democratic Party emails showing favouritism for Mrs Clinton in the primary threatens to deepen the perception that she prefers to play by her own rules.

Mrs Clinton was introduced by her daughter, Chelsea, who spoke warmly of her mother as a woman "driven by compassion, by faith, by kindness, a fierce sense of justice, and a heart full of love".

A parade of speakers - gay and straight, young and old, white, black and Hispanic - cast Mr Trump as out of touch with a diverse and fast-changing nation.

But Mrs Clinton sought to reach beyond the Democratic base, particularly to moderate Republicans unnerved by Mr Trump.

Former Reagan administration official Doug Elmets announced he was casting his first vote for a Democrat in November and urged other Republicans who "believe loyalty to our country is more important than loyalty to party" to do the same.

Following reports Russia hacked Democratic Party emails, Mr Trump said he would like to see Moscow find the thousands of emails Mrs Clinton deleted from the account she used as secretary of state.

Hours later, he told Fox News he was being "sarcastic", although shortly after his remarks on Wednesday, he tweeted that Russia should share the emails with the FBI.

Mr Trump attacked Mrs Clinton for not saying the words "radical Islam" in her speech.

"Our way of life is under threat by Radical Islam and Hillary Clinton cannot even bring herself to say the words," he said in a series of tweets.

Neither Mrs Clinton nor US president Barack Obama uses the phrase "radical Islam" because they say it is misleading, pointing out that the ideology motivating terrorists does not reflect true Islam.

But Republicans argue that the failure to use the label has hampered the fight against terror.

In her speech, Mrs Clinton said she would work to fight the radicalisation of young people in the US and abroad.