Well today is eventful. After news breaking just now of parcel bombs being sent to City Airport, Waterloo station and Heathrow comes news that all trains are blocked from Cannon Street at the time of writing.
So far nothing has left for 20 minutes. Southeastern are blaming a broken rail and not linking it to other issues mentioned above.
UPDATE: Trains have started running but in limited numbers.
The station is likely to close due to overcrowding and people are being urged to use the tube or other stations if possible.
More as it comes in.