We were about half an hour into the spectacular Fuerzabruta performance, when one of the big vertical acts - a sail likestructure with two performers on top - collapsed into half of the audience.
It was hard to work out what had happened at first, but we were quickly ushered out and it was clear something had gone very wrong.
Luckily, it sounds like there were no serious injuries"
More top news
Paramedics were on standby outside the police cordon as armed officers stood by the property.
A team of researchers has taken samples from the ten busiest London Underground lines to work out which are the dirtiest.
The action comes on top of an emergency timetable which has seen hundreds of trains a day being axed.