update a time honored tradition. security is tight in china s tiananmen square on the 25th anniversary of the crackdown on pro-democracy demonstrators. hundreds of people were killed in the incident. chinese leaders aren t allowing any memorial events, and they re trying to muffle all criticism. nhk world has the story from beijing. reporter: tee rnman square is crowded with tourists, but many police officers are keeping watch over the scene. officials have installed metal detectors at all entrances to the square. the police are frisking people for weapons. these measures have been in place since at least tuesday, but on wednesday, security officials began searching everyone s bags, as well. they ve also deployed more officers. and we can see police vehicles inside the square. the police questioned a british man who was taking pictures. he later told us he has been asked to show i.d. on three separate occasions. chinese officers blacked out the nhk world premium channel a