Google Inc. (GOOG) apologized Monday to a Chinese rival that complained its data were used by the U.S. search giant in a new Internet tool in an incident that highlighted the intense competition in China's booming online market.

Sohu.com Inc. complained Sunday that Google's tool for inputting Chinese characters appeared to copy material from Sohu's Sogou search engine.

Chinese Web surfers pointed out similarities shortly after the release of the Google tool.

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"We are willing to face up to our mistake, and offer an apology to users and to the Sohu company," Google said in a statement.

However, it gave no details of what Google did, and a spokeswoman said she had no additional information.

Web portals in China spend heavily on new search, entertainment and other features, and react quickly to competitive threats.

Inputting the nonphonetic ideograms in which Chinese is written is a time-consuming chore, and a system that offers more convenience could help a site draw traffic from competitors.

Google's tool, the Pinyin Input Method Editor, is meant to be an easier way for a user to input characters in Pinyin, a phonetic system for writing Chinese characters in the Roman alphabet. It suggests possible characters after just a few letters are typed.

Google, based in Mountain View, Calif., said its suggestions for characters are based on data gathered by Google's Chinese-language search engine about the frequency of searches for certain words.

But Sohu complained that Google also drew on similar data from Sogou.

The Google statement Monday noted that Web surfers have pointed out some material came from "non-Google data sources."

It gave no indication how much was from other sources or how it was included in the new Chinese-character tool.

China has the second-largest population of Internet users, with 137 million people online, and is on track to surpass the United States as the largest population in two years.

Google and other foreign Internet outfits are struggling to adapt to a Chinese market where communist leaders try to control what the public sees and limit foreign ownership of Web companies.

The Chinese writing system adds a layer of complexity for foreign competitors trying to tailor their systems for Chinese users.

Google is China's No. 2 search engine, with a market share of 21.7 percent, while industry leader Baidu.com Inc. has 55.2 percent, according to Shanghai research firm iResearch Inc.

Yahoo Inc.'s (YHOO) China portal is third with 7.2 percent and Sogou No. 4 with 6.5 percent.

Google launched a China-based service, Google.cn, after seeing its market share erode as government filters slowed access for Chinese users to its U.S. service.

Human-rights activists have criticized the new service, which excludes search results on human rights, the Dalai Lama and other topics banned by the communist government.

Market pressures have forced competitors to evolve quickly and embrace drastic changes.

The Chinese partner that operates Yahoo's China portal announced in January it was getting out of mainstream search due to intense competition and would become a business-oriented search engine.