North Korea's nuclear blast thrust President Barack Obama into an alarming new overseas crisis Tuesday, at the moment he hoped to use his annual State of the Union address to focus on jobs.

With a characteristic sense of timing, Pyongyang set off its underground nuclear test as Obama polished a new call for action at home to tackle high unemployment and economic headwinds threatening the fragile recovery.

Less than a month into his second term, the president will step up to deliver the annual showpiece speech in the House of Representatives, and before a huge national television audience at 9:00 pm (0200 GMT).

Obama will strike the populist message that helped him defy tough times to win re-election in an address largely aimed at a domestic audience -- a down payment from the stock of political capital he piled up in November.

But North Korea's test also presents Obama with a foreign policy headache in Asia, as Pyongyang shrugs off sanctions which have kept it in deep isolation to stride closer to full membership of the nuclear club.

Obama had already been under fire from political opponents over another nuclear imbroglio, with Iran, as he argued for more time for punishing sanctions to convince the Islamic Republic to halt its atomic development.

Ironically, Obama had been expected to renew his core commitment to seek cuts in global nuclear weapons stocks, which has been at the core of his foreign policy, during his speech on Tuesday.

North Korea's action once again revealed Pyongyang's penchant for using big events, like major Obama speeches or a current transfer of political power in South Korea, to issue a flamboyant demand for attention.

It also came as Obama nominees Chuck Hagel and John Brennan await confirmation votes to be the next chiefs of the Pentagon and CIA, after encountering opposition from Republicans.

The president will still likely use the bulk of the State of the Union speech to lay out a governing program to match the soaring progressive vision of his inaugural address last month, drilling down on the haunting jobs crisis.

"The President has always viewed the two speeches, the inaugural address and the State of the Union, as two acts in the same play," White House spokesman Jay Carney said, before word came of the North Korean nuclear test.

"The core emphasis that he has always placed in these big speeches remains the same and will remain the same, which is the need to make the economy work for the middle class."

Obama will refresh some plans he has already framed for creating jobs, including investment in America's ageing infrastructure -- which never made it past Congress -- and offer some new ideas.

But the speech will take place in the shadow of Obama's row with Republicans over huge budget cuts due to hit in March 1, which could hammer the fragile economy.

There are new reasons for alarm over the flat economy, after GDP contracted at an annual rate of 0.1 percent in the last quarter of 2012 and the unemployment rate ticked up to 7.9 percent.

The White House argues, however, that there is no comparison between the howling crisis that Obama inherited four years ago and the economy of today, although it does not dispute that many Americans are still hurting.

In a new Quinnipiac University poll released Monday, 53 percent of voters said they believed the economy was in recession, and 79 percent described it as "not so good" or "poor."

But Obama was still trusted, by 47 percent to 41 percent, to handle the economy better than Republicans.

While jobs will be his prime focus, Obama is also likely to highlight other domestic issues, though he knows Washington's bitterly partisan climate could render many big plans dead on arrival on Capitol Hill.

One priority will be building support for new laws to curb gun violence, after the horror of December's massacre of 20 small kids at a school in Newtown, Connecticut.

First Lady Michelle Obama will host in her box in the House the parents of Hadiya Pendleton, a teenager gunned down in a random shooting not far from the president's Chicago home days after she took part in his inaugural parade.

At least 23 members of the House will also host gun violence victims. Among them will be US lawmaker Gabrielle Giffords, who suffered brain damage after a gunman opened fire at one of her political events in 2011.

Natalie Hammond, a teacher who was shot three times by the Newtown gunman, will also be there.

Aides said Obama will also make a pitch for immigration reform, the centerpiece of his second-term agenda, amid signs that Republicans keen to mend fences with Hispanic voters may be ready for some rare cross-party compromise.

He may also note the impending return of the remaining 60,000 US troops in Afghanistan in 2014, but it is unclear whether he will offer more details on the pace of their withdrawal.