Outgoing US President Barack Obama bid farewell to Americans in an emotional speech here on Tuesday night with the same message of hope and optimism that brought him into the White House eight years ago.

From his adopted hometown of Chicago, the city where he found purpose in public life, the 44th President of the US called on the country to be “anxious, jealous guardians of democracy”, CNN reported.

While asking Americans to stay committed to democratic values and persist in their optimism for change, Obama also expressed warning for the years to come.

“Tonight it’s my turn to say thanks … Everyday I learned from you. You made me a better president, and you made me a better man,” the President told a crowd of about 20,000 people in an hour-long address.

“After eight years as your President, I still believe that.”

“And it’s not just my belief. It’s the beating heart of our American idea — our bold experiment in self-government,” the President told the American people in a large convention hall a few blocks from Grant Park, where he spoke to supporters on the night of his historic election in 2008.

He implored his backers to be vigilant in protecting basic American values that he warned could come under siege.

“Democracy can buckle when we give in to fear,” he said. “So just as we, as citizens, must remain vigilant against external aggression, we must guard against a weakening of the values that make us who we are.”

And he warned against turning inward, telling Democrats that only by involving themselves in a real political discourse could they hope to renew the hopeful vision he brought to the White House eight years ago.

He warned that “laws alone won’t be enough” in resolving persistent differences between Americans.

“Hearts must change,” he said.

The speech also reflected the unique situation Obama will confront as he leaves the Oval Office. At just 55, he is preparing for an active post-presidency in which he will champion many of the same core issues he worked on in the White House, including minority rights and opportunities for young people, the Los Angeles Times reported.

In 4,300 words, Obama also listed major feats his administration had accomplished during his tenure, including reversing recession, opening up a new chapter with Cuba, inking the Iranian nuclear deal, taking out Osama bin Laden, promoting gay marriage and increasing medical insurance coverage.

His successor, President-elect Donald Trump has vowed to undo some of his signature policies. He would be sworn into office on January 20.

The President also stressed solidarity despite a presidency sometimes at odds with the Congress.

“Democracy does not require uniformity,” Obama said. “Our founders quarrelled and compromised, and expected us to do the same. But they knew that democracy does require a basic sense of solidarity — the idea that for all our outward differences, we are all in this together; that we rise or fall as one.”

He said he has not abandoned his vision of progressive change but warned that it now comes with a new set of caveats.

Senior advisors said Obama knows that many progressive, religious and ethnic minorities and immigrants were feeling apprehensive with the approach of the handover to Trump, the Los Angeles Times reported.

Obama’s successor was elected after promising to crack down on immigration, scrutinise Muslims in the US and challenge what he termed “political correctness”.

He paid an emotional tribute to First Lady Michelle Obama, addressed his children, and thanked Vice President Joe Biden, who were all in attendance except younger daughter Sasha.

The President’s younger daughter is in Washington to prepare for an exam on Wednesday morning.

His voice quaked when describing Michelle’s contribution. “You took on a role you didn’t ask for and made it your own with grace and grit and style and good humour.”

“You made the White House a place that belongs to everybody,” Obama said to his wife.

The First Lady received a standing ovation, and a visibly overwhelmed President was seen wiping away tears when he addressed his wife as a “girl of the south side”.

Turning to his children, the “proud dad” said: “Malia and Sasha, under the strangest of circumstances, you have become two amazing young women.

“You are smart and beautiful, but more importantly, you are kind and you are thoughtful, and you are full of passion.

“Of all that I have done in my life, I am most proud to be your dad.”

The President then thanked Biden for serving alongside him in the White House, saying: “He is like a brother and family.”

As he spoke before a rousing crowd of supporters, Obama was interrupted often with screams of “I Love you Obama.”

A protester held aloft a “Pardon All of Us” sign, and chants of “Four more years” drowned out the shouts.

“I can’t do that,” Obama said when the crowd begged him to run again, which is not allowed by the Constitution.

Obama’s goodbye was a dramatic reinterpretation of a presidential farewell address, ending his speech with his signature “Yes, we can” concept that propelled him into the Oval Office.