A Google Inc. logo sits on display inside the Barcelona Growth Center in Barcelona, Spain, on Thursday, Feb. 20, 2014. Bloomberg News
China is ratcheting up scrutiny of foreign companies online ahead of the sensitive 25th anniversary of the Tiananmen Square crackdown Wednesday, presenting challenges to businesses that see it as a growth market.
Google Inc. GOOGL -1.55% 's search and other services remained inaccessible in China on Tuesday, in what one activist group says is a significant ramp-up of Beijing's blocks on the company. Anticensorship activist group GreatFire.org said it had observed an escalation in blockage of Google services in China, including search, Gmail, translation and "almost all other Google products."
Typically, the Mountain View., Calif., company's services are intermittently accessible in China. Google shifted its China-focused search operations to Hong Kong in 2010. "We've checked extensively and there are no technical problems on our side," a Google spokeswoman said.
Meanwhile, a LinkedIn Corp. LNKD +0.76% spokesman said local censorship requirements "have just recently been imposed upon us within China." The professional social-media site launched a Chinese-language version in February and has set up operations in the mainland.
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"We've long recognized that offering a localized version of LinkedIn in China would likely mean adherence to censorship requirements of the Chinese government on Internet platforms," said the spokesman, Roger Pua.
China Foreign Ministry spokesman Hong Lei said China manages the Internet "according to law," without elaborating.
China often limits access to some websites based outside China ahead of sensitive anniversaries or political meetings. The Google block coincided with a block of The Wall Street Journal's English- and Chinese-language websites. A spokeswoman for Dow Jones & Co., which publishes The Wall Street Journal, confirmed the Chinese site had been blocked since Saturday and the English-language site since Monday but declined to elaborate.
China's Internet censors have taken a more aggressive approach since President Xi Jinping came to power in 2012. Over the past year, the government has cracked down on online commentators, formed a high-level committee to address Internet security, and run an unprecedented antipornography campaign that led to the revocation of two online-publication and distribution licenses held by popular Internet portal Sina Corp.SINA +0.66%
LinkedIn in February said it planned to base servers and other operations in China. That allows it to offer greater services and lessen the chances of running into problems with Beijing. But such companies are then subject to Chinese laws.
"We are strongly in support of freedom of expression," said Mr. Pua. " But, as we said at the time of our launch in February, it's clear to us that in order to create value for our members in China and around the world, we will need to implement the Chinese government's restrictions on content, when and to the extent required."
He said the amount of information on LinkedIn filtered in China is minuscule because the service doesn't specialize in political topics.
Shaun Rein, the head of consulting firm China Market Research Group, said he received a notice last week from LinkedIn indicating he could no longer post to different groups on the site without first receiving approval by a moderator. Mr. Rein, who has been posting regularly on LinkedIn for about six years, said the change came after he posted about difficulties faced by U.S. firms in China following the back-and-forth between the two over cyberespionage.
"I've been backing up my contacts because I'm worried they'll block me and I won't be able to reach anyone," said Mr. Rein, adding that on LinkedIn "people are looking to show their knowledge and sell their services; if you can't have a discussion, that's an issue."
Mr. Rein said his firm has completed three projects for LinkedIn in the past. LinkedIn declined to respond to Mr. Rein's comments.
Google decided to stop censoring Internet searches in China in 2010 and shifted its Chinese search operations to Hong Kong. Since then its services in China have experienced occasional outages that the company has said can't be attributed to abnormal operations—a sluggishness that sometimes slows to a crawl during anniversaries or political meetings.
Pressures felt by both companies show how deeply concerned China's leaders are that access to information out of their control could be deeply destabilizing as the country faces a slowing economy, rising ethnic tensions and a degrading environment.
A surge in denial-of-service attacks have originated from China since Monday, according to CloudFlare, a company that provides Web performance and security services for more than a million websites. Denial-of-service attacks cause disruptions by overwhelming a computer or network with a high level of online activity. Usually the attacks originate from networks of computers that have been hijacked by malware or viruses.
CloudFlare Chief Executive Matthew Prince said it was difficult to tell the exact target of the attack. The company "saw them pick up a few weeks ago, then quiet off for a while. [The attacks] started back up again today," he said.
Write to Paul Mozur at paul.mozur@wsj.com