The controversy over curbs imposed by Beijing on Google that prompted it to quit the country, has surfaced again with a European Commission official saying that China's Internet "firewall" that is used to block online content constitutes a "trade barrier" under the WTO rules.

China's Internet "firewall" is a trade barrier and needs to be tackled within the framework of World Trade Organisation (WTO), European Commission vice-president and head of EU's digital agenda Neelie Kroes said in Shanghai today.

"It is one of those issues that needs to be tackled within the WTO," he said, adding the firewall is regarded as a trade barrier if it is used to block Internet content. Kroes, who served as the European Commissioner for competition until 2009, was speaking at the China headquarters of video-sharing company Tudou, a rival of Google's social networking platform YouTube which is blocked in China.

"I am pushing wherever I can just to get European enterprises a level playing field in China and the other way around. It should be reciprocal," Kores said, adding the amount of disruption from the firewall varies from business to business.

After a prolonged wrangle with the Communist regime, Google quit China and moved its Chinese language operations to Hong Kong, objecting to a Chinese law that requires Internet companies to block or remove objectionable content, including pornography and any information deemed sensitive by the ruling Chinese Communist Party.

Google still can be opened in China but with limited access as it has closed its Chinese search engine Google.com/cn and opened Google.com/hk.

Though China has over 400 million Internet users, all social interactive platforms like the YouTube, Facebook and Twitter are blocked apparently by the firewall.