Experts say US-Chinese relations could have worsened had the whistleblower decided to stay on the autonomous island

Edward Snowden's unexpected departure from Hong Kong threatened to sour US-Chinese relations further on Sunday, infuriating US officials whose extradition attempt was deftly deflected by the Hong Kong authorities.

The NSA whistleblower's dramatic flight came hours after US officials stepped up pressure on Hong Kong to arrest him, with one warning that delay would complicate bilateral relations. Snowden, 30, had previously said he would stay in the territory to fight his case.

Hong Kong authorities said the US request did not provide adequate documentation and added that Snowden left of his own accord through "a lawful and normal channel".

Pointedly, their statement also said they had formally requested a clarification from Washington of Snowden's claims that the US had hacked targets in the territory.

Even after Snowden's departure, a spokeswoman for the US justice department said it would continue to discuss the matter with Hong Kong as well as pursuing law enforcement co-operation with other countries where Snowden might attempt to travel.

But experts said that his decision had potentially prevented a more poisonous, intractable row between the US and China. Hong Kong is part of China but governed under the "one country, two systems" framework; it has considerable autonomy but Beijing retains ultimate responsibility for foreign affairs.

"I can imagine that even if he were not encouraged [to leave], information may have been leaked to allow him to leave before a warrant was issued," said Ronny Tong Ka-wah, a barrister and legislator for the pro-democracy Civic party.

Sunday's statement from Hong Kong authorities said the US had requested they issue a provisional warrant of arrest against Snowden, adding: "Since the documents provided by the US government did not fully comply with the legal requirements under Hong Kong law, [we] requested the US government to provide additional information so that the Department of Justice could consider whether the US government's request can meet the relevant legal conditions.

"As the [Hong Kong] government has yet to have sufficient information to process the request for provisional warrant of arrest, there is no legal basis to restrict Mr Snowden from leaving."

Simon Young, director of the Centre for Comparative and Public Law at Hong Kong University, described the news of Snowden's departure as "a shocker". He said: "The US government will be irate with their Hong Kong counterparts [and] may even question whether the Hong Kong government was acting in good faith pursuant to their treaty obligations. I have no doubt that they were, and it is quite common for government lawyers to seek more information on surrender or mutual legal assistance requests before local process can begin."

But Young noted that given the very low threshold for a provisional warrant, – evidence that the person was in Hong Kong and that he or she was wanted for prosecution in the US – Washington "will wonder why the Hong Kong government feels the surrender paperwork needs to be fully in place" at that stage.

Tong said: "From Beijing's point of view it is probably the most acceptable solution. If Beijing was to refuse to surrender Snowden that might harm Sino-US relations. On the other hand, if Beijing was to allow Snowden to surrender, it might well be subject to criticism both here in Hong Kong and in European countries making noises about the conduct of the US … [And] if it was put through the judicial process, it would be difficult to predict the outcome."

He added that for Beijing "it's far better to stay behind the scenes" than get involved publicly.

Regina Ip, a pro-Beijing legislator and former secretary of security, told the New York Times: "I think [the US] government will be upset for a while, but I hope that they will shrug it off, because our government acted in accordance with the law. Our government officials can breathe a sigh of relief."

Steve Tsang of the University of Nottingham noted Hong Kong's statement was "difficult for the Americans to counter — they can't just say 'Ignore the rule of law and arrest him because we asked for him.'"

Hua Chunying, a spokesperson for China's foreign ministry, said it had noted reports on Snowden's departure but was "not aware of the specifics". She said "the central government always respects the [Hong Kong] government's handling of affairs in accordance with law".

Her statement added that China was "gravely concerned" about details of fresh of Snowden's allegations by Snowden about Chinese targets – that the US hacked Beijing's prestigious Tsinghua University and Chinese mobile phone companies so it could access millions of text messages. "

We are gravely concerned about the recently disclosed cyber attacks by relevant US government agencies against China. It shows once again that China falls victim to cyber attacks. We have made representations with the US."

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