An unknown group in Japan has published a video on YouTube showing an incredibly elaborate prank – convincing people a giant robot is attacking their high-rise office building in Tokyo.

The Gundam Fever Project has published a 1min 50 sec video that shows how they set up the prank, replacing the windows in an office with projection screens pretending to the glass.

At the appointed time, the projection screens were set to project what looks like a massive 1:1 scale MS-06 Zaku II mobile suit from the popular sci-fi anime franchise series Mobile Suit Gundam standing outside the window.

Put together with convincing sound, light and smoke effects in the office, and you have a group of terrified employees.

No reason is given for why the prank was played but the group says it has more in store.