Three masked men in Sydney break-in

A family in Sydney's inner west has spoken about their terrifying ordeal after three men with a firearm burst into their home and robbed them of cash and jewellery.

A 21-year-old man was hit in the back of the head with the butt of the weapon after the masked men broke into the Marrickville house about 11pm on Wednesday, police say.

The other occupants, including an 83-year-old grandmother, were not injured.

The men stole numerous items including $5000 cash and designer handbags.

The mother of the 21-year-old was visibly shaken when she spoke to reporters outside her home on Thursday.

She said she thought the break-in was a wind-up at first, but then saw that "my son is shaking and he is crying", as reported on the Nine Network.