The Chinese-controlled Hong Kong administration today rejected a US request for the arrest of American whistleblower Edward Snowden, after which the ex-CIA operative left the former British colony to seek asylum in Cuba or Venezuela.

"Snowden has left Hong Kong through legal and normal means for a third country," the Hong Kong Special Administrative Region (HKSAR) said in a statement.

"The HKSAR government has informed the US government of Snowden's departure from Hong Kong," Chinese state-run Xinhua news agency quoted the statement as saying.

The US government's request for the Hong Kong government to issue a provisional arrest warrant for Snowden did not fully comply with the city's legal requirements, the statement said.

The Hong Kong government could not keep Snowden from leaving before getting "adequate information" to handle the provisional arrest warrant which it had asked the US side to offer, it said.

Significantly the Hong Kong government has also asked the US to explain the reported hacking of some computer systems in Hong Kong by the US National Security Agency for whom Snowden worked.

The government institutions will follow up related developments to safeguard the legitimate rights of Hong Kong residents, it said hinting that it would investigate his allegation of US cyber attacks on Hong Kong entities.

The statement came after 30-year-old Snowden left by an Aeroflot flight to Moscow on his way to Cuba or Venezuela today.

Observers say that though there was no mention of Chinese government, the foreign affairs of the Hong Kong government is controlled by Beijing and the administration's decision was taken with the consent of China.

Snowden, who stayed in the former British colony for 34 days revealed some of the most damaging details about US cyber espionage including snooping on US and as well as people all around the world besides carrying cyber attacks on China.

His arrest and subsequent extradition was rejected by Hong Kong despite an extradition treaty with US.

His defection proved to be a coup of sorts by China as he revealed a host of details about cyber attacks carried out by US on China, strengthening Beijing's assertions that it was a victim of hacker attacks from Washington, while the official Chinese media went ballistic on his allegations.

Reacting to the revelations made by Snowden, China's state-run Xinhua news agency today termed the US as the world's "biggest villain" for IT espionage.

"These, along with previous allegations, are clearly troubling signs. They demonstrate that the United States, which has long been trying to play innocent as a victim of cyber attacks, has turned out to be the biggest villain in our age," it said in a commentary.

Before Snowden left today, the Hong Kong-based South China Morning Post which has been getting exclusive interview with him carried a second instalment of his revelations alleging that US has hacked Chinese mobile phone companies to steal millions of text messages besides snooping on top Chinese university.

"There's far more than this. The NSA does all kinds of things like hack Chinese cell phone companies to steal all of your SMS data," he said in addition to his allegation that US carried out cyber attacks on number of Chinese institutions.

While alleging US hacker attacks on China, he has not provided any evidence in this regard.

Text messaging is the most preferred communication tool in mainland China, used widely by ordinary people and government officials from formal work exchanges to small chats.

Government data show that the Chinese exchanged almost 900 billion messages in 2012, the Post report said.

China Mobile is the world's largest mobile network carrier, with 735 million subscribers by the end of May.

China Unicom, the second-largest, has 258 million users while China Telecom comes in third with 172 million users.

Snowden also alleged that America carried out intensive and intrusive cyber attacks China's Tsinghua University in Beijing, which is widely regarded as China's top education and research institute.

It was the target of extensive hacking by US spies this year, Snowden told the Post.

It is not known how many times the university, which runs a number of China's research programmes has been attacked by the US National Security Agency (NSA) but details shown to Post by Snowden revealed that one of the most recent breaches was early as this January.

The information also showed that the attacks on Tsinghua University were intensive and concerted efforts.

In one single day of January, at least 63 computers and servers in Tsinghua University have been hacked by the NSA, the Post report said.

Snowden, who was accused by some of US officials as possible Chinese spy said the information he shared on the Tsinghua University attacks provided evidence of NSA hacking because the specific details of external and internal internet protocol addresses could only have been obtained by hacking or with physical access to the computers.

The new revelation comes a day ahead of the case filed by US officials formally charging Snowden.

The Tsinghua university is home to one of China's six major backbone networks, the China Education and Research Network (CERNET) from where internet data from millions of Chinese citizens could be mined.

The network was the country's first internet backbone network and has evolved into the world's largest national research hub, the Post report said.

It is one of China's non-commercial networks, owned by the Ministry of Education, but operated and maintained by the university and other colleges.