If you look at it alone, the power required by the laser will be only 5w laser, which is small. With more people staring, you probably should need more power, such as around 100.
The atmosphere of light will be considered when looking at it. If it is at dawn, using low beam will be futile. You may need more, about 50 or more.
Many people are attracted by the power of light, not by their gaze, and sometimes they use laser pointers on airplanes to get into serious trouble.