Alibaba Group, which operates China's biggest e-commerce site, said it is expanding its travel business to include international-airline-ticket sales and plans to take on China's largest online travel company.

Taobao.com, Alibaba's retail website, on Wednesday began selling tickets online for international flights and is aiming to undercut ticket prices of Ctrip.com International Ltd., the current market leader in China, and other competitors.

A Taobao spokeswoman said it would match the price of any non-Taobao listing for international air tickets and subsidize an additionaldiscount to attract buyers. 'By the end of the year, Taobao travel channel hopes to be selling 50% more airplane tickets than Ctrip.com's online ticket sales,' she said.

The move shows how China's Internet companies are increasingly competing in each other's niches. Several companies are developing search sites to compete with Baidu Inc., China's biggest search company. That includes Alibaba, which earlier this month agreed to buy a stake in Sohu.com Inc.'s Sogou search business. Baidu, meanwhile, is beefing up its offerings in e-commerce, online video and other areas.

Hangzhou-based Alibaba launched air-ticket sales on its website earlier this year. It hopes consumers will be attracted to a new buyer-protection policy, which offers a refund of up to three times the amount of any international air ticket sale in the event of a dispute.

A spokeswoman for Shanghai-based Ctrip said it doesn't consider Taobao a competitor. Ctrip said the two sites aren't comparable because Ctrip is a specialty site that fulfills travel bookings and handles after-booking services, while Taobao doesn't complete orders itself but rather is a platform that enables smaller ticket agents to sell online.

The company added that aggregating smaller agencies would inevitably lead to huge disparities in the quality of service.

Taobao has succeeded in undercutting competitors before. It began as a consumer-to-consumerauction site in 2003. When the company launched a campaign several years ago to overtake eBay Inc. in China, it allowed sellers to list products on its site commission-free, which in effect undercut eBay's fees. Taobao's popularityeventually surpassed that of eBay, which largely withdrew from the Chinese consumer-to-consumer market in 2006.

Taobao, which says 200 billion yuan (about $30 billion) of transactions were made through its site last year, continues to allow sellers to list and sell products without fees. It earns revenue from advertising and special listing services.

It also has aggressively expanded its business-to-consumerretail website, called Taobao Mall, that lets registered retailers, including travel agents, open online stores on its platform to tap what it says are 200 million registered users.

According to Taobao, more than 200 travel agencies and airlines have sold tickets on Taobao, and approximately 10,000 tickets are sold daily on the site. According to the Civil Aviation Administration of China, about 486 million plane trips were taken in China in 2009, about 37 million of which were international flights.

Online travel booking represents a relatively small portion of bookings in China's booming travel market. Ctrip, the largest air-ticketing agency in China, estimates it has an 8% to 9% share of the market, but most bookings are still done offline, since travelers tend to book at the last minute.

In a statement, Taobao said 'the travel sector is a very big market in China and as a new entrant . . . Taobao has a lot to learn and much to do in terms of improving the consumer shopping experience.'