In the past three years, Beijing has seen a growing number of labor disputes involving legal questions about employer-employee relationships.

Many of the disputes have centered on smartphone applications, as the mobile economy has developed rapidly, courts in the capital reported on Tuesday.

With more people working for increasingly prosperous internet platforms since 2015 - especially smartphone applications that provide car-hailing and food services - app operators have been taken to court more frequently, Beijing High People's Court said.

"Such new labor cases have been a challenge for our hearings, and the number is still going up," the court told China Daily, though it did not give an exact citywide figure.

On Tuesday, a report made by Chaoyang District People's Court said that it heard 188 such lawsuits from January 2015 to March this year; Haidian District People's Court concluded 55 such cases between January 2016 and February this year.

Different from traditional employment, the mobile app job is "flexible", said Wu Kemeng, a judge in Chaoyang. "Some app platforms without fixed workplaces are more like a bridge connecting customers and service providers, and many workers don't need a full day at work."

"That is to say, it's difficult to verify whether there is a labor relationship between the free workers and the app platforms. This is the focus of many lawsuits as well as the challenge in the hearings," he said.

"Some agreements between app operators and workers can only be regarded as cooperation or information sharing, which means the providers in these cases are not protected under the Labor Law," he said.

In June 2016, for example, the court rejected the claim of an employment relationship between 56 people and Mei Mei Da, a popular beauty app, because the workers had only provided nail-painting services in accordance with customers information collected by the platform.

"The workers made decisions on when and where to provide the services by themselves, and they didn't agree on salaries with the app operators," said Xiao Wei, another judge of the court. "In other words, the platform just shared clients' information with them instead of managing them."

She warned job seekers to be more careful, "as people without a labor relationship cannot get social insurance under the law".

"If an app platform requires a certain working time and place and has a system for governing attendance, its agreement with service providers may be more easily identified as a labor relationship," she added.

Wang Yan, a judge from Haidian district, suggested the city's labor administrations strengthen supervision of app platforms to prevent them from intentionally shirking their responsibilities or cheating job-seekers.

"As the apps bring more job opportunities, they must be better regulated," she said.