US President Barack Obama has hailed relations with China, saying the two countries have a huge stake in each other's success.
At a White House ceremony to greet Chinese leader Hu Jintao, he said the US and China would be more prosperous and secure when they worked together.
Mr Obama also raised the thorny issue of human rights.
Mr Hu said co-operation should be based on mutual respect, and they should respect each other's development paths.
The two leaders have now gone in for talks, which are expected to tackle issues from currency and trade to defence and security.
Meanwhile US officials revealed that a $45bn (£28bn) export deal had been signed with China, including Beijing's $19bn purchase of 200 Boeing aircraft.
'Universal rights'
The BBC's Paul Adams in Washington say the US administration is making sure this state visit lacks none of the required pomp.
After Mr Hu's arrival, the two leaders shook hands as the Chinese leader was welcomed with full military honours.
They stood on the White House lawn as a military band played the two national anthems accompanied by a 21-gun salute, then walked over to meet invited members of the public before addressing the crowds.
"We have an enormous stake in each other's success," Mr Obama said. "We will be more prosperous and more secure when we work together."
He cited President Jimmy Carter's meeting with Chinese leader Deng Xiao Ping in 1979 which normalised relations between the two countries, frozen for the previous 30 years.
He said the current visit would lay the basis for the next 30 years of ties.
He also referred to human rights.
"History shows that societies are more harmonious, nations are more successful and the world is more just, when the rights and responsibilities of all nations and all people are upheld. Including the universal rights of every human being," he said.
In response, Mr Hu said co-operation between the two countries in various fields had produced "fruitful results" and relations had "achieved new progress".
"Our cooperation as partners should be based on mutual respect," he said.
"We live in an increasingly diverse and colourful time. China and the United States should respect each other's choice of development path and each other's core interests. We should deepen mutual understanding through communication, increase mutual trust through dialogue and expand common ground through exchanges."
As the ceremony was going on, on the other side of the White House pro-Tibet demonstrators vented their anger against what they regard as a repressive regime, chanting: "Who is a liar? Hu Jintao is a liar" and "Killer,killer, Hu Jintao."
At a news conference later, Mr Hu is expected to face questions on China's human rights record.
'Tough talk'
Mr Hu arrived at Andrews Air Force base outside Washington on Tuesday and was greeted by US Vice-President Joe Biden before attending a private dinner at the White House hosted China and US pledge stronger tiesby President Obama.
As Mr Hu dined, activists outside the White House held aloft banners urging the US president to to "admonish Hu" over China's human rights abuses.
Western TV reports of Mr Hu's trip broadcast in China were blacked out when the crowds of protesters were shown - one BBC report showing footage of human rights protesters demonstrating outside the White House was blacked out for 30 seconds.
The White House is laying on a full formal reception with lunch at the state department, dinner at the White House, and meetings with some of America's most powerful business leaders from firms like General Electric, Coca-cola and Boeing.
