Police are on the hunt for a group of men behind a terrifying home invasion in Sydney's northwest.

Seven men were armed with an axe, knife, hammer and gun when they broke into a home on Purser Avenue, Castle Hill, about 1am Thursday.

They threatened six occupants before stabbing an 18-year-old man in the stomach several times.

Officers were told the men demanded property from the people inside.

A seventh occupant, a 17-year-old boy, was in the backyard at the time and was smashed across the head with a hammer.

The group stole six mobile phones before damaging the home and fleeing the scene in a car.

Paramedics treated the injured men at the scene before they were rushed to Westmead Hospital. Their conditions are unknown.

Detectives launched a widescale land and air search for the seven men who remain on the run.

Investigations are ongoing.

Police will address the media with more information later on Thursday.

Originally published as Teen stabbed in horror home invasion