Twitter gives an astonishing immediate insight into events in another city. Our thoughts are with those the police say are killed and injured in Manchester this evening. From eye witness reports and pictures posted on the internet, this is what I can tell so far.

There certainly was at least one large explosion, and this was consistent with a bomb. But a bomb was not the only possible explanation. however contrary to reports, the bombs does not appear to be inside the Manchester Arena.

I am somewhat handicapped as I do not know how to post short pieces of video from Facebook onto the blog. But the best evidence of the explosion so car is this video apparently from a nearby car park.

These two frames are a fraction of a second apart. It is much plainer on the video than on these stills, but in the second a huge flash of light has gone off behind the building. The area of rising ground or low structure immediately to the left of the building is more lit in the second frame, and the aurora of city light in the sky above the building is lighter and reaches further. The back of the building would be substantially illuminated. As I say, the flash is much more obvious in live action than in comparing the two frames.

A little less than a second after this flash, a major rumble is heard. This is a loud explosion. Given that from the gap between the light and the sound it is over half a mile away, it is really a big explosion.

UPDATE I now have a video I can post and you can plainly see the flash just before the sound reaches the camera. Just to the left of the building shows it best. This explosion was not confined inside.

But it is not within the Manchester Arena itself. There are plenty of photos and again videos from inside the arena.

The video from which this still is taken, for example, is apparently after the explosion because there is a certain amount of panic and screaming going on. But the video pans round the entire indoor arena and nowhere is there a sign of any damage, certainly not commensurate with the size of the explosion, and certainly nothing which would affect the integrity of the walls and ceiling sufficient to emit that great flash of light outside. Also an explosion of that size, if a bomb, would emit a very large amount of smoke, and there is very not enough smoke at all in this indoor area (there is a very little haze, but more consistent with concert pyrotechnics or dry ice). Finally, while there are the first signs of panic, an explosion of that size would have caused vastly more panic if it had not been some way distant. Most people are still holding their balloons.

There are many pictures of lobby areas too but none of these shows bomb damage or smoke either.

The dominant narrative now seems to be a nail bomb or bombs inside the arena. Nail bombs typically are not on the scale of the explosion caught outside. A nail bomb might be consistent with the lack of major damage inside the arena and lack of immediate generalised panic, but it is not consistent with the big bang and flash visible outside. It is of course not impossible there was one or more small nail bombs inside and a further bomb outside. But it is also possible the explosion was outside and the inside injuries due to panic and crush.

We should avoid jumping to conclusions on the cause, and if it is a bomb we should avoid jumping to conclusions on who planted it. There is terrible tragedy in Manchester tonight, the worse for affecting young people. But my trawl through social media also revealed a fantastic communal spirit, with ordinary people looking after each other, opening up their homes, running people around in their cars and helping reunite families. It is also excellent how many Manchester people are reacting against those trying to use this to promote racial or political agendas. I pray the number of casualties proves to be not as bad as first thought.