Bill Ackman says "regional banking system is at risk".

Ackmann tweet.

Ackman is a hedge fund billionaire.

Catching up to the news flow:

Yikes, we are seeing some panic on this:

• US regional bank PacWest is considering strategic options, including a sale

Its hit markets:

• Its getting hot in herre. Gold spike up, oil spike down

And, its moved beyond the rumour stage:

• US bank Pacwest - advisers engaged to mull on alternatives, including potential sale