The latest incident has sparked concern over the safety of increasingly popular but loosely regulated hire cars. In this photo illustration, a woman uses the Uber app on an Samsung smartphone on September 2, 2014 in Berlin, Germany. Getty Images/Adam Berry

SHANGHAI (Reuters) - Chinese police have arrested an Uber driver suspected of robbing and molesting a female passenger at knifepoint, state media reported, sparking concern over the safety of increasingly popular but loosely regulated hire cars.

A spokeswoman in China for the San Francisco-based company behind the ride-hailing app did not answer repeated phone calls on Thursday or reply to an email requesting a comment.

Safety concerns over the country's ride-hailing app market came under the spotlight in China in June when a driver was detained for sexually assaulting a drunk female passenger who had used an app to get a hire car.

The latest assault happened in Chengdu, in the western province of Sichuan, at about 2 a.m. one night several weeks ago when a 42-year-old female passenger hailed a Uber car, the Chengdu Business News said in a report republished on the website of the state news agency Xinhua.

The driver pulled a knife on the woman after suddenly stopping in a tunnel and robbed her of more than 5,000 yuan ($780) in cash, it said.

He then drove to the outskirts of town where he molested the woman, snapped some photos and warned her he would make the pictures public if she went to the police, the report said.

She waited about two weeks before reporting the attack on Aug. 9. The suspect was detained two days later, it said.

He was arrested on Wednesday on suspicion of robbery and "forcible molestation of a woman", it said.

Such incidents elsewhere have damaged Uber's reputation and sparked both public and regulatory backlashes against online car-hailing services.

The New Delhi government banned Uber in December after a woman passenger accused one of its drivers there of rape. A court later rejected the ban, saying the state could strictly regulate app-based taxi companies but that it did not favor an outright ban.

The main players in China's ride-hailing app market include Didi Kuaidi, backed by Internet giants Tencent Holdings Ltd and Alibaba Group Holding Ltd, as well as a range of smaller players including Yidao Yongche.

In addition to stiff competition, Uber has faced regulatory challenges in China with occasional office raids and crackdowns on drivers.

News of the Chengdu attack raised some alarm online.

"I don't dare take those cars!!!! And fortunately I'd never take a car at night," one user posted on China's Twitter-like Weibo microblog.

Another said: "You can never know who's behind the mask in hire cars."