The Obamas praised Clinton as “a leader we all trust” and rebuked Republican candidate Donald Trump as “unqualified”.

“He lacks abasic understanding of the world,” Obama said.

The country’s first black president tried to maximise his appeal to his African American compatriots, urging them to get out and vote for Clinton in the general election, as well as support the Democratic Party in the US Senate and Congress elections.

Obama then welcomed Hillary Clinton to the podium, describing her as his “most effective” Secretary of State.

Clinton asked voters to choose the values she stands for, and promised to unite a country polarised and torn in the bitter presidential race.

“We have to bridge the divides in our country,” she said. “I regret deeply how angry the tone of the campaign became.”

Clinton joked about Trump attacking her for having no stamina, saying she stood next to him for four-and-a-half hours, which proved she had the stamina to be the president and commander in chief.

Rock stars Bruce Springsteen and Jon Bon Jovi also performed at the Clinton rally. Meanwhile, in New York, Madonna gave a surprise concert in Washington Square Park in support of Clinton.

Supporters in Pennsylvania, one of the key battleground states, as well as from elsewhere on the east coast started queuing at Independence Mall around noon. When the door opened at four o’clock, the end of the line extended approximately 1.6 miles from the entrance of the mall, and was still growing.

Admissions were very slow because of the huge size of the crowd and strict security checks. As darkness fell and the temperature dropped rapidly, vendors walked down the line selling Clinton campaign souvenirs and some of those in the queue ordered pizza or Chinese takeaways to eat while they waited.

Li Wei, a Chinese immigrant who has yet to be naturalised waited in line with his wife and their two children. He said he had arrived in the country only months ago and was curious about the whole election culture.

Facing them stood two young men holding a handwritten Trump sign and urging people not to go any farther for Clinton. Later a pickup truck filled with Trump signs and flags drove slowly down the street, to be met with boos and jeers from the Clinton supporters.

“I couldn’t believe there are still nearly half of the people here who want Trump,” said a former federal employee who claimed he would only vote for a “sensible candidate”.

Steven Jackson, a Pennsylvania University student who is originally from New York, a solid Democratic State, said he had moved his registration to Philadelphia and would go early to a polling station on Tuesday morning to avoid a queue such as this. “A vote counts for much more here,” he said. “A non-vote is just a vote for Trump.”

Elaine Fowler, a pensioner who travelled from New Jersey to join the rally, said she supported Clinton because she was the most qualified candidate.

Anisha Chirnule also planned to vote for Clinton, citing the former secretary of state’s political experience; inclusive attitude towards lesbians, gays, bisexuals and transsexuals, and her concern for human rights.

“Having a female president also matters for us feminists,” said Chirnule, a 28-year-old who attended a woman’s college in Philadelphia.

At 8.30pm, the scheduled finish time of the rally, the venue was full but tens of thousands of people remained outside the security fence, chanting Clinton’s name.

Additional reporting by Stuart Lau