US Democrats are gathering in Chicago to celebrate Vice-President Kamala Harris’s campaign for the White House against Donald Trump and to honour President Joe Biden, whose exit from the race turned his party’s fortunes around.

The four-day Democratic National Convention has also drawn thousands of pro-Palestinian protesters opposed to the Biden administration’s support for Israel’s Gaza offensive.

However, the rally turnout on Monday (local time) was measured at a few thousand, not the tens of thousands that had been predicted.

Biden, 81, touched down and will give a prime-time address at the convention later on Monday to make the case for electing Harris and defeating former president Trump, 78.

As Democrats seek to project a sense of unity after the unprecedented switch in candidates, Harris, 59, is likely to join Biden on stage, where he will ceremonially pass the torch to her.

Harris will formally accept the nomination on Thursday night (US time) with a highly anticipated speech.

Former New Zealand prime minister Jacinda Ardern will be in attendance, a spokesperson confirmed.

Along with her attendance, Ardern would be involved in a side event at the national convention, the spokesperson said.

If elected on November 5, Harris will make US history as the first female president.

A coalition of some 200 social justice organisations, many from pro-Palestinian groups, will gather outside the convention.

Some pro-Palestinian delegates are pushing for the Democrats to change their platform to limit weapons to Israel.

Harris heads into the convention riding a historic whirlwind: Her campaign has broken records for fundraising, packed arenas with supporters, and turned opinion polls in some battleground states in Democrats’ favour.

Biden abandoned his re-election bid after his disastrous debate against Trump on June 27 prompted long-time allies, major donors and other party supporters to demand he step aside.

Polls a month ago showed Trump with a clear lead over Biden. Harris has closed the gap nationally and in many of the highly competitive states, including Pennsylvania, that will play a decisive role in the election.

“I’ve been to every convention since I was able to vote, and I can say I’ve not felt this kind of energy and electricity at any convention other than the one for Barack Obama,” Democratic Illinois Governor JB Pritzker said on CNN’s State of the Union on Sunday.

Harris went on a bus tour in western Pennsylvania on Sunday with her running mate, Minnesota Governor Tim Walz.

During the tour she suggested Trump was a coward whose politics focused on putting down rivals.

She will be in Chicago for much of the week but will make a side trip to Milwaukee on Tuesday for a campaign event, returning to Chicago to hear her husband, Doug Emhoff, address the convention that night.

Meanwhile, the Trump campaign will barnstorm key battleground states to try to steal the spotlight away from Harris and highlight some of the policy issues where Republicans hold a polling advantage.

Trump will deliver remarks on economic policy at a small business in southern Pennsylvania on Monday before events in North Carolina, Michigan, Arizona and Nevada later in the week.

Some major allies and donors have urged Trump to steer clear of racial and gender-based insults on Harris and focus his attacks instead on her policy record.

Trump’s Michigan event will be in Howell, a city struggling to move past its racist history, including Ku Klux Klan rallies in the 1970s and 1980s.

In July, about a dozen white supremacists chanted “Heil Hitler” during a march through Howell, while another group of demonstrators shouted “We love Hitler, we love Trump” from a highway overpass in a nearby town.

The Harris campaign has criticised Trump for refusing to condemn a “blatant display of racism and anti-Semitism in his name”.

A Trump campaign spokeswoman said the former Republican president would emphasise in Howell that hate would have no place in the country if he returned to the White House.

Democrats will also pay tribute on Monday to their failed 2016 presidential candidate, Hillary Clinton, who is expected to speak before Biden.

Former presidents Barack Obama and Bill Clinton will speak on Tuesday and Wednesday, respectively.