China's stock market is suffering in the post-attack slump
Mr Tang is to meet separately with President George W Bush and Secretary of State Colin Powell on Friday.
He told US Vice-President Dick Cheney on Thursday that China was willing to upgrade its anti-terrorism co-operation with the US in the wake of the attacks, the official Chinese news agency Xinhua reported.
But he reiterated Beijing's position that the United Nations Security Council should approve any military action.
The attacks on the World Trade Center and Pentagon "show that international terrorism has become a serious threat to world peace and stability," Mr Tang said.
"International co-operation is both necessary and pressing. China stands ready to enhance dialogue and co-operation with the US," he said.
New priorities
Correspondents say that the attacks will completely change the agenda of Mr Bush's planned trip to China.
The visit was expected to be tense amid serious differences over Taiwan, Tibet and missile defence - and coming on the heels of the dispute over the US spy plane forced down in China in April. But now it will probably focus instead on the international response to terrorism.
China may hope to deflect US criticism of its human rights policy by aiding Washington against militants.
But an unnamed State Department official told the French news agency AFP that there would be no link between the issues.
"We don't regard the attacks as affecting other aspects of our relationship," the official said.
China has its own concerns about Islamic militants, with an insurgency in the north-western Xinjiang Uighur Autonomous Region.
Chinese dilemma
In the wake of the attacks on 11 September, China said it wanted to see "concrete evidence" against potential targets before it would support a US military strike against those suspected of involvement.
The BBC's Beijing correspondent, Rupert Wingfield-Hayes, says the Chinese Government is in a difficult position.
On the one hand, it would very much like to see the destruction of terrorist networks run by the likes of Osama Bin Laden and other groups based inside Afghanistan, because Muslim separatists operating within its own borders are thought to be getting support from Afghan-based groups.
On the other hand, China has been implacably opposed to the US or Nato intervening in what it calls the internal affairs of other countries.
China, for example, strongly opposed Nato intervention in Kosovo two years ago, and refused to support the US-led coalition during the 1991 Gulf War.