I was only 17 at the time, but I remember watching BBC and they had a small message come up at the bottom of the screen saying a plane had collided with one of WTC. Shortly afterward, they interrupted the programme to go straight to BBC News.
I didn't know how a plane could accidentally crash into a tower, but after they talked about it for a while, I was thinking surely it wasn't an accident. Aircrafts just don't fly themselves into skyscrapers.
3 weeks before, my parents had come back from staying at the Marriot at WTC.