Man arrested after Sydney shop robbery

A man has been arrested after an alleged armed robbery of a convenience store in Sydney's west.

The man allegedly threatened an employee at the Emerton store with what appeared to be a firearm on Saturday morning before fleeing with SIM cards and food.

Soon after the 5.30am robbery, police were called to a nearby unit where a man was being held by residents.

It's alleged the 29-year-old broke into the residence and tried to steal a car before he was apprehended.

He was taken to Mt Druitt Hospital for mandatory blood and urine testing after crashing a car.

Police say that on his release from hospital he will be assisting with inquiries into both incidents.