LAS VEGAS (AFP) - Hillary Clinton fired up a crowd during her first major rally in months after a strong Democratic debate performance, vowing to back President Barack Obama's immigration reform efforts.

Smiling and appearing relaxed, the Democratic frontrunner carefully avoided references to her opponents, especially her strongest rival, Senator Bernie Sanders.

"I really don't like what the Republicans are saying about immigrants," the former secretary of state told supporters on Wednesday (Oct 14).

"We are a nation of immigrants, built by immigrants.

"Immigration is who we are, look at us."

Reform of America's immigration system has been a hot-button issue of the 2016 presidential campaign.

Republican candidate Donald Trump, a billionaire real estate developer who has never held elected office, has stoked the fire by vowing to expel immigrants illegally in the United States and to build a wall on the US-Mexico border, if he's elected.

He has also proposed repealing the constitutional right to citizenship of anyone born on US soil.

Clinton accused her Republican rivals of "doing a great damage to our nation by their insults and their attacks." "So as your president, I will certainly work hard on an immigration reform," she promised, vowing to preserve the executive orders President Barack Obama issued to ease deportations of certain groups of immigrants.

- 'Feeling lucky' in Vegas -

Earlier, Clinton scored an endorsement from the International Union of Painters and Allied Trades.

"I'm feeling really lucky in Las Vegas," Clinton joked after visiting a union training facility.

"Getting the endorsement of this union and the members you represent, and what it means to really focus on the trades - it doesn't get any better than that."

Turning to the economy, Clinton focused on her plans to boost employment and raise wages.

"We're gonna start by creating more jobs by actually investing in putting people to work to build and maintain our roads, our bridges, our airports," Clinton said.

She vowed to change the tax system so that "the wealthy pay more and give the middle class a tax cut." "It's time we start rebuilding the middle class," Clinton added.

About 2,500 people gathered at a nature reserve in Las Vegas to see Clinton, according to her security service. Many carried banners supporting the candidate.

"The toughest part is going to be the primary, and it won't be like last time (in 2008) because this time she has a huge amount of the minority vote because Barack Obama took a lot of the minority vote," said retiree Tony Kouffman, 75.

Clinton's strong debate performance on Tuesday saw her deftly parrying her rivals' attacks on her political judgment and her 2002 vote for the Iraq war.

That left her the undisputed frontrunner less than four months before the first votes are cast in the Democratic primary race.

"One of the reasons it was good is because we were actually talking about what a president should be doing to make sure you have the support you need to make the most out of your lives," Clinton told supporters.

Retired teacher Nancy Haag, said Clinton's decades of experience as first lady, senator and top US diplomat mean she has what it takes to be the next president.

"I expect to see the next woman president," Haag said. "I like her honesty and her consistency and her willingness to do whatever it takes to move the country forward."