@@mandolinsara Yes. this sound is used when something great happened and NHK's all channels (including radio and Satellite broadcasting) start broadcasting the news. This was also used in outbreak of Gulf War.
Probably been forgotten, but I think it's more of the staff pressing the button multiple times to make sure the newsroom around the world to receive it. While in Japan it would be received right away (hence multiple overlaid repeats of the chime) overseas newsroom might have longer delay and take the repeat of the chime as heavily urgent news is coming Just like during gulf war, when the telex of the newsroom starts ringing, they will stop all regular programming and go to the news studio for it, at least that's one of my opinion. Nowadays they'd probably use something along the way of BBC's news ingest/reuters news service style of system rather than telex/chime system like this
An interesting thing to note is that there is a rarely used American equivalent to this dating back to the 40s, for NBC. Most people know NBC’s iconic jingle (G-E-C), but on very urgent/important news (mainly used back in WWII), the final note would play a second time (G-E-C-C)