North Korea on Wednesday readied a historic party conference to bolster its young new leader as the US demanded the country call off a planned rocket launch in favour of a 'better future'.

The conference of the communist Workers' Party is expected formally to install Kim Jong-Un, who succeeded his late father in December in nuclear-armed North Korea's second dynastic succession, as party secretary-general.

It is only the party's fourth-ever special conference and will kick off events leading up to Sunday's 100th anniversary of the birth of North Korea's founding leader Kim Il-Sung, the new supremo's grandfather.

The North's propaganda machine Wednesday cranked up tributes for Kim Jong-Un, who is in his late 20s.

The Workers' Party daily Rodong Sinmun, in an editorial, acclaimed him as a 'heaven-sent general and great leader'.

"The historic conference of the Korean Workers' Party that opens today will demonstrate thoroughly the party and people's iron will and unwavering faith in following the path of victory led by dear comrade Kim Jong-Un," it said.

Tens of thousands in the tightly regimented state have been sprucing up the capital Pyongyang for mass anniversary festivities. The centerpiece of the commemoration is a rocket launch scheduled for between Thursday and Monday.

North Korea says the rocket will propel a satellite into orbit to collect data on forests and natural resources within its territory. But the West says it is a disguised ballistic missile test, in violation of a United Nations ban.

China, North Korea's sole diplomatic and economic patron, and Russia have also expressed concern about the launch. US Secretary of State Hillary Clinton on Tuesday said North Korea faced a clear choice.

"We are consulting closely in capitals and at the United Nations in New York and we will be pursuing appropriate action," she said at a news conference with Japanese Foreign Minister Koichiro Gemba, who echoed her remarks.

"If North Korea wants a peaceful, better future for their people, it should not conduct another launch that would be a direct threat to regional security," Clinton said.

Japanese defence forces have deployed missile batteries in central Tokyo and dispatched destroyers to shoot down the rocket if it threatens Japan's territory.

Vessels have been warned to stay out of shipping lanes that might fall under the rocket's path, while at least three airlines -- Japan Airlines, All Nippon Airways and Philippine Airlines -- are diverting some routes.

But North Korea insists that the rocket poses no danger to countries in the region, and says it has every right to launch the rocket.

"The right to have a satellite is a universal right of every nation on this planet," Ryu Kum-Chol, a senior member of the communist state's Committee for Space Technology, said in a rare briefing for foreign journalists Tuesday.

"We do not recognise any UN resolution that violates our sovereignty," he said. So far Kim Jong-Un has been formally appointed to only one of his late father's posts -- supreme commander of the 1.2-million-strong military, the world's fourth largest.

The promotion to party secretary-general would show he is more firmly in charge. And an annual session of North Korea's rubber-stamp parliament on Friday could elevate him to chairman of the National Defence Commission, the top decision-making body that was previously chaired by Kim Jong-Il.

"Dear comrade Kim Jong-Un is the highest leader of the party, military and the people who is bringing the ideology and accomplishments of the great leaders Kim Il-Sung and Kim Jong-Il to a shiny completion," Rodong Sinmun said.