As mysteriously as it began, blocking by Chinese authorities of the Internet search engine Google was suddenly lifted Thursday.

Users in Shanghai and Beijing reported that they could once again view Google, widely used by China's 30 million-plus Net users because it has a powerful feature for finding Chinese-language material online.

Starting about Sept. 1, those trying to reach the site began finding themselves rerouted to heavily censored, less effective search engines run by private Chinese Internet companies.

"I'm thrilled that Google is back," said one user in a chat-room on the Web site of the People's Daily, the official Communist Party newspaper. "Google, I love you!" said another posting.

Chat-room users had bitterly criticized the ban. Analysts said popular outcry and pressure from businesses that rely on Web tools like Google for research may have persuaded Beijing to reverse the restrictions quickly.

"The Internet has seemed to prevail," said Duncan Clark, managing director of BDA China Ltd., a Beijing-based Internet consulting firm.

AltaVista, another U.S. search engine that had been similarly rerouted, remained blocked on Thursday, though rerouting had ended.

In its usual secretive way, Beijing made no announcement of the new measures and refused to confirm their existence, or their lifting.

But analysts and users linked the interference to a Communist Party congress in November.

Dissent is usually more tightly muzzled before political events of this size. This congress is particularly sensitive because a new generation of leaders is expected to begin taking over.

Authorities apparently targeted Google and AltaVista because they don't filter material deemed subversive from their search results, as the Chinese sites must.

Still, analysts said the brief period of rerouting had demonstrated authorities' growing technological capabilities.

Another new censorship technology remained in place. Users this week have begun complaining of an increase in selective blocking -- being able to visit Web sites but not being able to see specific articles or other content of a politically sensitive nature.

Both new technologies appear an effort by authorities to strengthen Internet barriers to subversive and pornographic material -- China's so-called Great Fire Wall.