The crew of a US spy plane today left China on board a chartered jet after a face-saving Sino-American deal was hammered out to secure their release after 12 days in captivity.

The Continental Airlines Boeing 737 took off from the southern Chinese island of Hainan at 7:30am (0930 AEST) for the five-and-a-half hour flight to the US Pacific territory of Guam, an AFP reporter said.

The plane is due to refuel at Andersen Air Force Base in Guam before heading on to the headquarters of the US Pacific Command on the western US island of Hawaii where the crew will be debriefed.

The 24 crew of the EP-3 Aries surveillance aircraft were seen entering the charter jet at an airport in the Hainan provincial capital Haikou wearing green aviator jumpsuits.

They were whisked from the military guest house in Haikou where they were being held in two minibuses with darkened windows accompanied by a convoy of security vehicles with flashing lights.

The media was kept far away from the crew members who made no comments before leaving.

The release of 21 men and three women came after China and the United States yesterday defused a stand-off triggered by a collision between the EP-3 and a Chinese fighter jet in international airspace off Hainan on April 1.

The US aircraft made an emergency landing on Hainan after suffering damage in the collision, which also led the Chinese jet to crash into the South China Sea.

The tense stand-off came to an end after US Ambassador Joseph Prueher handed Chinese Foreign Minister Tang Jiaxuan a letter saying Washington was "very sorry" for the loss of Chinese pilot Wang Wei in the incident.

The letter also said the US side was sorry the EP-3 landed at Lingshui military base on the southern tip of Hainan without permission.

But it refrained from meeting China's original demands to apologise and accept responsibility for the collision, and to stop surveillance flights off the Chinese coast.

The letter said military officials from both sides would meet on April 18 to work out how the collision occurred and how to return the damaged US plane, which was packed with valuable high-tech spying equipment.

"We can't wait for them to get home," US President George W Bush said just before the charter jet left China.

Earlier Bush reiterated US "sorrow" over the loss of the Chinese pilot, who parachuted into the South China Sea but has yet to be found despite an enormous search.

Tense negotiations to end the crisis centred on finding a semantic compromise which would satisfy China's demand for an apology and the US insistence it had nothing to apologise for.

And both sides claimed the agreement as a victory.

A strident editorial in the People's Daily, the mouthpiece of China's ruling Communist Party, said the statement was a fully-fledged apology.

"Our government and people have carried out a staunch struggle against American rule by force and compelled the United States to change its rude and unreasonable hard line attitude and apologise to the Chinese people," it said.

But US Secretary of State Colin Powell was adamant the US letter was not an apology and that Washington would never apologise for the mid-air collision.

"To apologise would have suggested that we had done something wrong and were accepting responsibility for having done something wrong, and we did not do anything wrong," Powell told a press conference in Paris.

Throughout the crisis China accused the EP-3 of deliberately ramming one of two Chinese fighter jets shadowing its movements, a version of events disputed by the United States.

Washington has said it cannot say for sure what happened until it has debriefed the spy plane's crew.

But the Pentagon has said the US plane was flying steady on autopilot and that downed Chinese pilot Wang Wei twice flew dangerously close to the US aircraft minutes before the collision.