President Donald Trump used a prime-time address to the nation Tuesday to insist on $5.7 billion for a steel wall along the Mexican border that he said would stop the shedding of "American blood" by illegal immigrants.

The nine-minute speech from the storied Oval Office in the White House contained no concessions to Democrats refusing to fund wall construction.

It also offered no hope for a quick end to a government partial shutdown triggered by the row that has left 800,000 federal employees without pay.

However Trump did steer away from earlier predictions that he might announce a national emergency, which would have given him the power to authorise the wall project without congressional approval.

Trump spoke in an unusually measured voice, apparently hoping to claim the moral high ground, and said he wanted to end the partisan divide in what has become a defining battle of his presidency.

"I have invited congressional leadership to the White House tomorrow to get this done. Hopefully, we can rise above partisan politics in order to support national security," he said. "This situation could be solved in a 45-minute meeting."

Despite that softer tone, Trump also spent much of the speech doubling down on his controversial message that illegal immigration along the US-Mexican border is above all a threat to the lives of Americans.

He listed gruesome examples of crimes committed by illegal immigrants, including a "beheading and dismembering," and said he would "never forget the pain" of survivors he'd met.

"How much more American blood must we shed before Congress does its job? For those who refuse to compromise in the name of border security, I would ask to imagine if it was your child, your husband, or your wife whose life was so cruelly shattered and totally broken," he said.

That, to opponents, is at best fearmongering for political purposes -- or race baiting at worst.

Democratic leader Nancy Pelosi said in her instant rebuttal speech that the real problem was Trump's "cruel and counter-productive policies" making the border ever more dangerous for vulnerable migrants, including young families.

Trump has said he will not sign spending bills funding swaths of government unless Democrats first agree to his wall. His speech showed no indication of giving way.

Pelosi, the speaker of the House of Representatives, said that meant Trump is "holding the American people hostage."

Chuck Schumer, the Democratic leader in the Senate, accused Trump of governing "by temper tantrum" and using government workers "for leverage."

NOT BUDGING

There had been speculation that Trump might give way, for example lowering the sticker price for the wall, or offering Democrats flexibility on other areas of immigration policy.

However, it was also significant that he did not announce a national emergency, which would have theoretically given him the right to charge ahead alone, getting the money from the military.

Democrats and some Republicans had warned that this would be seen as a dangerous escalation of the row and would be challenged in court.

Despite those warnings, Trump and his aides repeatedly floated the possibility in the run-up to the address, which was Trump's first ever from the Oval Office.

"He's not saying yes or no," top advisor Kellyanne Conway told journalists at the White House a few hours earlier. He's "considering it," she added.

HISTORIC STAGE

The Oval Office has witnessed many historic announcements, ranging from George W. Bush's reaction to the 9/11 attacks to John F. Kennedy's televised appearance at the height of the Cuban missile crisis.

Trump's gambit was that the solemn setting will allow him to regain the momentum on the Mexico wall issue that helped him get elected in 2016 and has become an obsessive goal for supporters.

He will follow up with a rare trip to the Mexico border itself on Thursday.

But with many Americans far from sold on Trump's lurid claims about illegal immigrants posing an overwhelming safety threat, the speech faced its own high barrier: credibility.

NOT ALL EYES ON PRESIDENT

While political junkies were fixated on the policy issues in the standoff, others took a rather less decorous view of the proceedings.

Betting site bookmaker.eu was offering odds for wagers on whether Trump would lie during his speech, declare a national emergency or end the government shutdown by January 18.

And Stormy Daniels, the pornographic film performer and stripper famous for claiming she was paid off to keep quiet about an affair with Trump, proposed another way to keep entertained.

"If you're looking for anything even remotely worth watching tonight at 9pm EST, I will be folding laundry in my underwear for 8 minutes on Instagram live."