US President Barack Obama and Chinese leader Hu Jintao sparred over human rights but smoothed over sharp differences and a dearth of breakthroughs by vowing to work to build trust.

On a long-awaited state visit, Hu made the unusual comment for a Chinese President that "a lot" remained to be done on freedoms in China, but pointedly did not share Obama's definition of universal human rights.

Later, the two presidents swapped the dry language of diplomacy for a gala state dinner, sprinkled with stars such as action hero Jackie Chan and singer Barbra Streisand, in White House rooms bathed in purple and red lights.

"While it is easy to focus on our differences, in cultures and perspective, let us never forget the values that our people share," Mr Obama said in a toast to Hu, pointing to mutual hard work, sacrifice and love of family.

Earlier, trumpets sounded and a 21-gun salute blasted over Washington as Hu arrived at a White House draped with US and Chinese flags, in the most sumptuous pageantry a US President can muster.

But at a frank press conference, there were few signs the leaders had ended disagreements on the rate of China's yuan currency, access to Chinese markets or strategic issues.

Both sides however promised to seek further cooperation on the world's most pressing issues and Mr Obama welcomed China's rise as a key power and looked forward to an era of "friendly competition."

The President also candidly laid out US differences with China.

He called for a level playing field for US firms, saying the yuan was undervalued, and encouraged dialogue with the Dalai Lama's representatives over Tibet.

Mr Obama acknowledged China had a different political system than America, but said he would not shirk from raising rights issues.

"We have some core views as Americans about the universality of certain rights — freedom of speech, freedom of religion, freedom of assembly — that we think are very important and that transcend cultures," he said.

"I have been very candid with President Hu about these issues."

Later, a senior US official said Mr Obama had personally raised the case of Liu, jailed in 2009 on subversion charges. He did not detail Hu's response.

Pressed by reporters on human rights, Hu said China had made "enormous progress", but his was a vast nation with many social and economic development problems.

"We do believe that we also need to take into account the different national circumstances when it comes to the universal value of human rights," he said, but admitted "a lot needs to be done in China in terms of human rights."

Earlier, US officials revealed that China would announce a mammoth 45 billion dollars in export deals with Washington, including a purchase of 200 Boeing passenger jets worth an estimated 19 billion dollars.

The order will bolster Mr Obama's bid to convince Americans that his ambitious foreign policy can have a domestic payoff in the wake of the deepest economic crisis in decades. Officials said the deals would support 235,000 US jobs.

And as both sides sought to enhance economic ties, Mr Obama hosted a meeting with Hu and top US business leaders, including executives from Microsoft, Motorola, Goldman Sachs, General Electric, Coca Cola, Boeing and HSBC.

Mr Obama said he hoped Beijing and Washington could ease recent trade frictions and break free of "old stereotypes."

The United States made no apparent progress however on its drive to see China's yuan firm faster against the US dollar.

China's currency policy "has not been substantially changed" by a meeting of Chinese and US leaders Wednesday, deputy foreign minister Cui Tiankai said.

Speaking after Mr Obama urged Hu to let the yuan strengthen faster against the greenback — a measure that could curb Chinese exports — Cui said the longstanding policy of a gradual appreciation would remain.

Mr Obama also used the press conference to say that both he and Hu wanted North Korea to halt "further provocations," and agreed that total denuclearization of the peninsula was the "paramount goal."

In a joint statement, both sides expressed concern at North Korea's uranium enrichment program, the first time that Beijing had made such concerns public.

Mr Obama and Hu stressed the need for improved inter-Korean relations to ease tensions and agreed that "sincere and constructive dialogue" between the two countries was essential.

South Korea welcomed the summit statement by the US and Chinese leaders, saying they supported Seoul's stance in setting terms for dialogue with North Korea.

Top members of Congress, including John Boehner, the speaker of the House of Representatives, declined invitations to attend the state dinner.

Democratic US Senate Majority leader Harry Reid even branded Hu a "dictator," before withdrawing the remark.