A gang has severed the hand of a young man during a brutal attack on a family home.

Four men are believed to have broken into the home on Banksia Ave, Greenacre, western Sydney, just before 2am on Saturday.

The 23-year-old was confronted and struck by the machete-armed group, which amputated his left hand.

Superintendent Rodney Hart said the group then threatened the man’s father and demanded cash.

“They forced him back into the main bedroom where a safe was located, it was opened by the victim and a large sum of money has been stolen,” Hart said.

The gang then drove off in a dark-coloured SUV before emergency services arrived at the home.

Paramedics treated the young man at the scene before rushing him off to hospital where he underwent emergency surgery.

Four other occupants in the house — a man and woman in their 40s and two males aged 16 and 19 — were not injured.

Police believe the attack was targeted due to a large amount of money from a business being held at the home.

“This is a brutal, violent attack which is extremely traumatic for the family,” Hart said.

A young man has had his hand severed during a ‘brutal’ home invasion in Greenacre.A young man has had his hand severed during a ‘brutal’ home invasion in Greenacre. Credit: 7NEWS

“There is no indication that this is related to any organised crime.

“Somehow these people were aware that there may have been cash on the premises and that’s what’s been targeted, but unfortunately this has been a brutal home invasion where this young man will have received life-altering injuries.”

A large presence of forensic investigators and police were seen scouring through the home in the hours after the attack.

Anyone with information has been urged to contact Crime Stoppers.

-With AAP