Twitter traffic on the hashtag #SOTU has exploded since US President Barack Obama started delivering his final State of the Union address, with more than 761,000 tweets using the tag, up by roughly 500,000 since Obama's speech began.

Jeers at House Speaker Paul Ryan's lack of participation counted heavily among the tweets. According to social media analytics firm Zoomph, #PaulRyan was among the top hashtags during the speech.

Ryan appeared only to have applauded Obama when the president mentioned US military personnel.

Author and New York Times columnist Anand Giridharadas (@AnandWrites) tweeted: "After curing cancer, we should cure the problem that prevents Paul Ryan's hands from joining even for things he agrees with. #SOTU."

Obama symbolically had a chair left empty in the box where First Lady Michelle Obama was sitting in honor of those who have died from gun violence. The hashtag #EmptySeat was trending heavily on Twitter in response to the gesture.

Obama apparently has delivered on his promise to keep this year's speech shorter: The text of his speech unofficially comes in at 5,438 words versus 6,776 in his 2015 speech.

The White House released a post by Vice President Joe Biden explaining his new task, heading an initiative to find a cure for cancer.

President Barack Obama was expected to detail Biden's role during the State of the Union speech Tuesday night.

Separately, however, he said claims that the ISIS fight is World War III are "over the top." Still, he urged Congress to pass authorisations to use military force against ISIS.

Obama, who is delivering his last annual speech to Congress before leaving office next January, said political discourse was meant to be messy, but - in an apparent nod to proposals by Republican candidates such as Donald Trump - required "bonds of trust" between citizens.

President Barack Obama touted his record on the economy and health care.

"More than 14 million jobs, nearly 18 million people now with health coverage -- together, we've pulled ourselves out of yesterday's crisis to put us on a stronger course for tomorrow," Obama said in the message posted at www.whitehouse.gov.

"Tonight I'll lay out a vision for an economy that's even stronger, a country that's safer, and a union that's more perfect.

"Because with one year left in my presidency, I'm still fired up and ready to go."

Still, Obama said his speech will stay focused on the future.

"The future we want - opportunity and security for our families; a rising standard of living and a sustainable, peaceful planet for our kids - all that is within our reach," will say.

President Barack Obama made a brief appearance on Facebook on Tuesday as he finalised the text of his last State of the Union address.

The president, sitting at his desk, said he was making last minute changes and added touches to his speech.

"There's a lot of work that still needs to be done," Obama said, adding that he wanted to make sure that the American people understood his proposals. "We've got some big choices ahead," he said. Hardly a quiet few hours for the White House in the run up to President Obama's swan song State of the Union address later on Tuesday.

Millions of Americans were discussing President Obama's upcoming State of the Union address on Tuesday on top social media platforms like Facebook and Twitter, debating anticipated speech topics such as gun control, terrorism and healthcare. US President Barack Obama voiced regret for failing to unite Washington since taking office on a wave of hope in 2009, as he prepared to give a State of the Union speech on Tuesday to launch his final year in the White House.

Asked about his inability to heal America's political divisions, Obama told NBC's "Today" show, "It's a regret."

The president planned to speak optimistically about America's future in his speech in Congress, one of his few remaining chances to capture and hold the attention of millions of Americans before the Nov. 8 election of a new president who will take office next January.

The Democratic president will give his final State of the Union address as campaign rhetoric for November's presidential election intensifies with candidates fighting over illegal immigrants, wage inequality and violence. President Barack Obama said he could envision Republican presidential candidate Donald Trump giving a State of the Union address - but in a comedy skit.

In a "Today" show interview ahead of his final State of the Union address, the Democratic president was asked if he could envision Trump, the billionaire developer known for his bombastic style, making his own State of the Union speech as president.

"Well, I can imagine it - in a 'Saturday Night' skit," Obama said, referring to the NBC's long-running late-night comedy show "Saturday Night Live."