Uber’s market-leading China rival, Didi Chuxing (formerly Didi Kuaidi), today announced the official launch of its new Internet bus-booking service, which it says will be fully integrated into the main app.

Didi just nabbed China’s first Internet car-booking license earlier this month, and says it plans to expand beyond just buses into what it calls the “mass-commute and tourism space” — it pegs China’s public bus market at nearly $16 billion.

“Didi Kuaidi users will now be able to search bus routes, book tickets, and initiate new routes seamlessly through its main app,” Didi said in a statement. “This new fully integrated solution further expands Didi Kuaidi’s one-stop mobile transportation platform that already provides taxi-hailing, online car-booking, chauffeur and ride-sharing services.”

The service has been launched following an earlier test version on China’s hugely popular chat app WeChat. That test ran in Beijing and Shenzhen back in July, and was aimed at professional commuters between 20 and 40 years old.

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Didi said the trial saw an 80 percent customer retention rate during the trial itself, which ran 1,500 bus rides per day across more than 700 customized routes. The company is already claiming over 500,000 Didi Bus users.

But there is a catch — using Didi Bus in China will cost three to five times more than taking public transport. That may not be an issue for the rising middle class and foreign tourists, but it may be enough to put off at least some Chinese commuters. The fact is, it’s unlikely Didi is targeting them anyway.

“Didi Kuaidi plans to increase investment in Didi Bus in new cities and routes, with the intention of complementing existing public transportation systems,” Didi said.

“The bus service is a key strategic step in Didi Kuaidi’s mission to build a comprehensive product platform that captures the diverse market demands with efficient, flexible and environmentally-friendly transportation solutions for China’s ongoing urbanization process,” it concluded.