Police are investigating the circumstances surrounding an armed robbery of a post office at Emerton this afternoon.

About 3:25pm, Thursday 2 August 2012, three men wearing balaclavas entered the post office on Jersey Road.

The trio, who were armed with a shotgun and knife, threatened staff before being handed a sum of cash.

They ran from the store and fled in a silver Holden Commodore which was last seen travelling west along Jersey Road.

A number of customers were in the store at the time but did not sustain any physical injuries.

A 90-year-old woman was treated at the scene by paramedics for shock and taken to hospital as a precaution.

Mt Druitt Police are in attendance at the post office and have established a crime scene which is being examined by officers from the Forensic Armed Robbery Unit (FARU).

Detectives are continuing their investigations into the robbery and are attempting to establish if there are any links to an earlier robbery of a hotel at Plumpton this morning.