Pony.ai, one of China's most valuable driverless car start-ups, has launched an app that allows users to hail an autonomous taxi, making it one of the first companies to do so.

The app, which was quietly launched in late December, allows a user to hail a self-driving taxi from a pre-set location in Nansha, which is part of Guangzhou in southern China. The car can travel to specific areas that have been set by the company such as its offices or residential areas.

Currently, only employees and a few VIP users are using the app, which is a mini-program built within WeChat, China's most popular messaging service. Rides are free for now.

Pony.ai, a $1 billion firm co-located in China and the U.S., makes software to power driverless cars. It does not make the vehicle itself. Instead it has partnered with automakers including China's BYD and GAC.

The company's technology relies on continuous testing and data gathering to improve the software, something that will be boosted by an autonomous taxi service carrying real passengers.