He described the US move as "a step in the right direction".
But he added that the crew had broken international law, and were now being questioned over the incident.
He repeated the Chinese Government's insistence that the United States "assume full responsibility" for the incident over the South China Sea.
On Wednesday, Mr Powell called the incident "a tragic accident" but stopped short of issuing the full apology demanded by Chinese President Jiang Zemin.
'Not enough'
In what appeared to be a conciliatory remark, the spokesman told news reporters that Beijing did not want the event to affect relations between the two countries.
He went on to repeat, however, that the US had made a mistake and should "make an explanation to the Chinese people".
Mr Sun said Beijing would allow US officials access to the 24 crew members only if the US adopted a "co-operative approach". He did not elaborate.
US diplomats on Hainan Island said that they had not been allowed to visit the crew on Thursday.
Earlier, the Chinese ambassador in Washington said there could be no solution to the impasse until the US accepted responsibility.
Speaking after a meeting with Mr Powell, Ambassador Yang Jeichi said an American apology was "very, very important".
The two men have agreed to continue with negotiations.
Mr Powell's statement appeared to be designed as a way out from the stand-off, using a form of words that went some way towards meeting Chinese demands and assuaging Chinese anger.
President George W Bush, for his part, has demanded the early release of the American plane and its 24 crew members.
Retaliatory measures
BBC Washington correspondent Paul Reynolds says that if this approach is not successful, the administration is likely to draw up a list of possible retaliatory measures.
These could include:
However, the major sanctions will be taken only as a last resort and very reluctantly.
The aim from the start has been to settle this as quickly as possible without grovelling to or humiliating China.
Hardened position
Chinese leaders, hardened their position on Wednesday when President Jiang Zemin personally repeated a demand for a US "apology".
But the US government remains adamant in refusing an apology, which might imply the military crew of the EP-3 surveillance aircraft had acted in error in patrolling the Chinese coast and engaging in "listening" activities.
"The accident took place over an international airspace, over international waters, and we do not understand any reason to apologise," White House spokesman Ari Fleischer insisted.
The US Navy EP-3E Aries II electronic surveillance aircraft landed on Hainan Island after being damaged in the collision off southern China.
The Chinese fighter aircraft crashed into the sea and its pilot is missing, presumed dead.
Crew members of the American plane are understood to have told US military attaché Brigadier General Neal Sealock about the destruction of the top secret information when they met him on Tuesday.
This allays fears in the US that American codes might fall wholesale into Chinese hands - but it is unclear whether all sensitive information was actually destroyed.