The Chinese activist group GreatFire, which operates websites that circumvent the country's censorship, said its online service has come under attack in an effort to shut it down.

"We are under attack and we need help," the group said in a blog post on Thursday, claiming it has been hit by a barrage of automated requests known as a distributed denial of service (DDoS) attack.

"This tactic is used to bring down Web pages by flooding them with lots of requests -- at the time of writing they number 2.6 billion requests per hour. Websites are not equipped to handle that kind of volume so they usually 'break' and go offline."

GreatFire allows residents of China to circumvent the so-called "Great Firewall" that censors much content from the West, by providing "mirror" websites of those which are blocked by censors.

The blog said the attack appears to be in retaliation for a Wall Street Journal article this week which explained methods to access censored websites.

"This attack affects all of our mirror websites," the blog said.

"While we have talked openly about our method of using collateral freedom to unblock websites and mobile apps that have been blocked by the Chinese authorities, the WSJ story clearly stated how the strategy works and how it is being used successfully to deliver uncensored content into China. Blocked websites that we have liberated in China include Boxun, Deutsche Welle and Google."

GreatFire said the increased data requests could lead to costs of up to $30,000 per day. It was seeking contributions to upgrade its servers to stave off the attacks and asking supporters to contact the hosting service, Amazon, to waive the extra costs.

"We've upgraded to faster servers and used other techniques to manage the load and it's working for now but we fear that the attack may be intensified at any time."

The news coincided with the apparent blocking of Reuters news websites in China, the latest Western news organization to face the issue.

Reuters said its sites in both English and Chinese were inaccessible in China on Friday, joining those of Bloomberg News, the New York Times and the Wall Street Journal.

China's Communist Party oversees a vast censorship system -- dubbed the Great Firewall -- that aggressively blocks sites or snuffs out Internet and TV content and commentary on topics considered sensitive, such as Beijing's human rights record and criticisms of the government.

Popular social network sites such as Facebook and Twitter are inaccessible in the country, as is YouTube.

Reuters websites blocked in China
Beijing (AFP) March 20, 2015 - Reuters news websites were inaccessible in China on Friday, the latest Western news organisation to be blocked in a country where censors keep a tight grip over information.

Attempts by AFP in China to open the agency's English- and Chinese-language websites returned only an error message saying that the page "can't be displayed".

Reuters said in a report that users first experienced difficulties accessing the sites late on Thursday.

China's Communist Party oversees a vast censorship system -- dubbed the Great Firewall -- that aggressively blocks sites or snuffs out Internet and TV content and commentary on topics considered sensitive, such as Beijing's human rights record and criticisms of the government.

Popular social network sites such as Facebook and Twitter are inaccessible in the country, as is Youtube.

Several Western news organisations have accused China of blocking access to their websites in the past, including the New York Times, Wall Street Journal and Bloomberg.

Reuters said Friday access to its websites had been cut off "at times," often after the publication of stories about which "the Chinese government is sensitive".

"Reuters is committed to practising fair and accurate journalism worldwide," it quoted an unnamed spokeswoman as saying in a statement.

"We recognise the great importance of news about China to all our customers, and we hope that our sites will be restored in China soon," she added.