Chinese activist site Greatfire.org which masks censored traffic into the country is under a sustained distributed denial of service (DDoS) attack that is racking up $30,000 a day in server costs.

The website masks internet traffic from websites including Facebook and Google, so it can be seen in China, and does so using cloudy servers. Attempts by Beijing to take down access to those content providers would incur an unpalatable amount of collateral damage, the activists contend.

Website admin Charlie Smith says the DDoS attack is delivering 2.6 billion requests an hour.

"We are under attack and we need help," Smith says.

"This kind of attack is aggressive and is an exhibition of censorship by brute force.

"Attackers resort to tactics like this when they are left with no other options."

Amazon has not yet said if it would waive the extra costs. The Register has contacted the company for comment.

Smith says the website's first-ever DDoS attack is likely prompted by a Wall Street Journal story published Wednesday (regwalled).

The DDoS is a 2500 increase on normal traffic levels and is slamming all GreatFire website mirrors of websites blocked on the mainland.

Beijing has stepped up pressure on the website in recent months, the activists say. The Cyberspace Administration of China labelled GreatFire a foreign "anti-China website" and has pushed its unspecified technology partners to cut ties, GreatFire alleges.

The site has upgraded to faster servers to handle the traffic influx but Smith fears it could sink if the attacks increase.

Smith is asking DDoS boffins to offer advice on mitigating the attacks.

The attacks are the latest GreatFire alleges to be the handiwork of Beijing. In November the activists said authorities used DNS poisoning against its content delivery network EdgeCast which caused mass outages and service interruptions.

The activists further claim that attackers recently attempted to intercept its encrypted email. ®