China’s Didi Kuaidi, the company behind the country’s two dominant taxi-booking apps, has raised $2 billion in its latest round of funding.

Reports surfaced a month ago that the company, backed by Alibaba and Tencent, was looking to raise $1.5 billion to fend off an aggressive move by Uber to invest CNY7 billion ($1.1 billion) in China this year and expand operations from 11 cities to more than 50 cities.

Didi Dache (Taxi) and Kuaidi Dache are the two leading taxi apps in China and merged back in February to create Didi Kuaidi, the world’s largest smartphone-based taxi service valued at an estimated $6 billion at the time. The company continues to run separate apps but has combined their technology and data.

The latest funding round values the company at an estimated $15 billion and was led by Capital International Private Equity Fund and Ping An Ventures, while a number of existing shareholders also took part.

Didi Kuaidi had previously raised $1.6 billion, including a $600 million round in January and another $142 million in May.

The company is able to avoid the regulatory problems that some of its competitors have faced by employing existing taxi drivers, VatorNews reported. China has an estimated two million taxi drivers, with as many as 1.5 million on the Didi Kuaidi network.

Didi Kuaidi operates in 360 cities in China and claims more than 200 million users, who take four million trips a day using the service.