Subway trains on Line 6 in Beijing are testing a smart service system that includes inspection cameras and LED windows showing useful transport information to passengers.

The system, called Intelligent Passenger Service System, provides convenience and care services for passengers, according to its developer.

As part of the system, some high-definition cameras are installed in train carriages, used to capture passengers' unusual conditions, such as whether they are wearing face masks or if somebody falls in a faint or waves for help, Li Yujie, deputy head of Beijing Subway's Technical Department, said in a video report by the Beijing News.

High-definition screens also can be seen from areas over the train's doors, showing different information, including lines and the degree of crowding in neighboring carriages, the report said.

Also, the train's windows, combined with LED panels, can dynamically show current locations, subway routes and maps of incoming stations.

"For example, passengers can see where toilets, elevators and exits are at the next station, and also what commercial facilities the station is close to," Li said.

The windows are called "magical windows" by passengers who have experienced the train.

The smart systems and functions will be further improved in the future, he said.