Edward Snowden, the former United States National Security Agency (NSA) contractor who is wanted for leaking details of a massive government surveillance programme, was allowed to leave Hong Kong Sunday.
The Hong Kong government said a US request for his extradition did not meet legal requirements and Snowden could not be prevented from leaving.
The Hong Kong-based South China Morning Post reported that Snowden boarded a commercial flight to Moscow, destined for "a third country". The Aeroflot Flight SU213 from Chep Lap Kok airport was scheduled to land at Shermetyevo International Airport, the newspaper said.
Documents provided by the US government, which has charged Snowden with spying, "did not fully comply with the legal requirements under Hong Kong law," the Hong Kong government said.
"As the 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 Hong Kong."
The former British colony has been a special administrative region of China since 1997, retaining rights to free speech and assembly.
Snowden's departure came after he revealed in an interview with the South China Morning Post that US authorities had hacked into Chinese mobile companies and a major Beijing university.
"The NSA does all kinds of things like hack Chinese cell phone companies to steal all of your SMS data," Snowden was quoted as saying in the report late Saturday.
Chinese state media on Sunday called on US to "come clean" over the full extent of its cyber espionage programme.
The US had also targeted Tsinghua University, Snowden told the South China Morning Post. The top Chinese research institution hosts one of the major backbone networks for the country's internet, and could enable access to internet data from millions of Chinese citizens, the newspaper said.
Evidence provided by Snowden showed the latest breach was in January this year, according to the report.
Snowden also told the newspaper that the NSA had hacked into computers at the Hong Kong headquarters of Pacnet, which owns one of the region's largest fibre optic submarine cable networks. The hacking took place in 2009, he said.
"Washington should come clean about its record first. It owes too an explanation to China and other countries it has allegedly spied on," China's official Xinhua news agency said in a commentary.
The revelations demonstrated the US, "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.
The commentary is one of the strongest-worded responses yet in Chinese state media to Snowden's allegations, in the absence of any detailed reaction from Beijing.
Chinese and Hong Kong officials have remained largely silent about Snowden's allegations.
The Central Propaganda Department is believed to have instructed Chinese media and websites to avoid or delete comments on the Snowden affair except those from Xinhua, according to the US-based China Digital Times website.
Snowden left the United States in May.