SAN FRANCISCO/SHANGHAI - Google Inc blamed "the great firewall" of China for blocking its Internet search service in the country on Tuesday, but said it did not know if the stoppage was a Chinese technical glitch or a deliberate move in their face-off over Internet censorship.

Whichever it was, the incident underscored the vulnerability of Google's business in the world's largest country.

Google said search traffic in China now appeared to be back to normal following its confirmation earlier on Tuesday of reports that many users in China were unable to search on its Hong Kong-based website.

In an unusual development, however, Google provided a new statement about the disruptions to its search service that reversed the explanation it had offered just three hours earlier.

Google said in an updated statement on Tuesday that changes it made to its search code, which it had initially cited as the cause of blocked searches in China, had been made a week ago, and not in the past 24 hours, as Google had first said.

"So whatever happened today to block Google.com.hk must have been as a result of a change in the great firewall," Google said in an emailed statement, referring to China's technology for filtering Internet content.

Asked if the "change" was a glitch or deliberate, a Google spokeswoman replied: "We don't know."

The news comes with Google's Chinese search service already in the headlines due to a censorship dispute with Beijing.

The company shut its mainland Chinese portal Google.cn last week and rerouted searches to its Hong Kong site in order to offer uncensored search results.

Analysts and China experts have been on the lookout for signs that Beijing might clamp down on Google and restrict its services, following harsh official comments in reaction to Google's new approach to offering Internet search in China.

Separately, Google also said its mobile services in China were partly blocked on Sunday and Monday.

Inconsistency in Google's search service to Chinese users could expose a weakness in Google's plan to provide search from Hong Kong, said Pacific Crest Securities analyst Steve Weinstein.

"If that continues you'd imagine that they would slowly over time lose share," Weinstein said.