A major police operation is underway in Sydney's west after a man was shot dead on a suburban street.

It's understood the man, aged in his 40s but yet to be formally identified, was shot and killed on Factory Street in Granville at 4.30pm.

Despite the efforts of first responders, he was unable to be saved.

READ MORE: Man paralysed in police van reaches $45 million settlement 

9News helicopter footage shows a heavy police presence at the scene and a number of paramedics.

Granville is about 18 kilometres from Sydney's CBD. 

A crime scene has been established and investigations are underway into the circumstances surrounding the shooting.

Any witnesses or anyone with information is urged to immediately come forward.

More to come..