Ground sunk in last couple of days!!

Hi
I'm not sure if i'm in the right area for this but i was in the kitchen this morning and was looking out of the window and i noticed a crack in the concrete step about an inch and a half wide.
I looked around this and there was a couple of bricks adrift from the surrounding wall and the gound looked like it had sunken.

When i went out of the back door the area of around 15 feet had cracks in the concrete about an inch wide, I could lift parts of the concrete out around the drain. It all seems to have just had a drop off virtually overnight.
I have looked around the house but no cracks apparent and the sinking is around 6 feet from the kitchen any help would be appreciated.
I have added some photo's aswell. View media item 26126 View media item 26127 View media item 26128

You probably got a leaking drain First thing is see if youre covered on your house insurance

Thanks for the reply and i am beginning to think that, Had all the drain covers up and watched the flows and they seem to be working ok.
I have sent some rods down them and there doesn't seem to be any blockages as such.

The only one that has water in is the rainwater drain from the guttering pipe which should leak off eventually.

The pipe may have a crack in it and over the years has sunk that section i will have to ring the insurance company monday and see whats what.

Those cracks look years old, are you sure they are recent?

Anyway, consolidation of the fill around the manhole can cause this.