A police incident was under way at Liverpool Street station in East London, with reports saying up to 30 police officers, some armed, have just rushed into the station.
A number of people took to Twitter to express their shock at the heavy police presence.
Thomas Chetwin tweeted: "9 met police cars just piled into Liverpool Street station."
And Twitter user @mrjoshuahh tweeted: "At #liverpoolstreetstation and 15 police officers armed with assault rifles arrived in 9 cars....
