Aiming to figure out how best to guard against possible terrorist attacks targeting large gatherings, the MPD has been testing a range of security devices at big events in Japan.

At the Tokyo Marathon 2015, police officers with wearable cameras on their heads ran the marathon course alongside other runners as they kept watch for suspicious individuals. Real-time video of the course were sent from the cameras to officers at the event's security headquarters.

With wearable cameras improving year by year, the so-called running police officers at this year's Tokyo Marathon were able to check the videos from their own cameras using wrist watch-type devices.

The MPD hopes that the wearable cameras will include face-recognition functions in the future so that they can automatically detect wanted people and other security risks registered on databases.

At the Sumida River Fireworks Festival in central Tokyo last summer, the Tokyo police tested a crowd behavior analysis system for detecting unusual incidents in congested places.

Security cameras for detecting suspicious items were installed at the time of the 2016 Group of Seven Ise-Shima summit in central Japan. (Jiji Press)