NSA whistleblower Edward Snowden has told a Hong Kong newspaper that the U.S. government has been hacking Hong Kong and Chinese networks for at least four years.

The comments were made as part of the South China Morning Post's exclusive interview with Snowden — his first since revealing himself on Sunday.

Snowden reportedly showed reporter Lana Lam documents that showed the NSA had been hacking computers in Hong Kong and on the mainland since 2009. He estimated there were hundreds of targets in Hong Kong and mainland China, including the Chinese University of Hong Kong. None of the documents revealed any information about Chinese military systems, Snowden said.

“We hack network backbones – like huge internet routers, basically – that give us access to the communications of hundreds of thousands of computers without having to hack every single one,” Snowden told Lam.

China's own online espionage efforts were put in the spotlight earlier this year after a report from U.S. security firm Mandiant that accused military-linked groups of hacking major U.S. companies. After that story, China hit back saying Washington was the "real hacking empire."