A pizza shop worker has suffered serious injuries after being shot twice during a robbery in Sydney's west.

Police said a 21-year-old male worker at a Domino's Pizza shop in Wentworthville was confronted in the early hours by a man carrying a gun and demanding money.

The employee was shot in his chest and hand during a fight with the man.

He was taken to Westmead Hospital in a serious condition.

Officers said multiple crime scenes have been set up as they investigate the shooting.

The gunman has not been found.

A Domino's spokesperson said the Wentworthville store was closed until further notice.

"An armed thief approached staff about 1:30am this morning, demanding money before one team member was shot," the spokesperson said.

The chain said they would provide support to the victims of the robbery.

Anyone with information about the robbery or the shooting should come forward, NSW Police said.