The 39-year-old man died shortly after emergency services were called to a home in Riverstone about 12.30am on Sunday following reports of a home invasion, NSW Police said in a statement.

A group of at least five males entered the home and allegedly stabbed the 39-year-old man before fleeing, police have been told.

"It is early in the investigation, but that is one of the lines that we are pursuing, that it was a targeted attack or that the offenders were known to the deceased or the deceased knew the offenders," Superintendent Jenny Scholz told reporters in Sydney on Sunday.

Police have found a firearm and a knife away from the home, she said.

"I cannot confirm we have the murder weapon at this stage," Supt Scholz said.

Two women, aged 34 and 43, were also in the home at the time.

The younger woman had some minor injuries and was treated at the scene, Supt Scholz said.

Two individuals apparently left the property on foot while three men drove away in a vehicle, Supt Scholz said.

A police helicopter, the riot squad and dog unit searched the area and arrested two male teenagers - aged 16 and 17.

Both were on Sunday charged with murder and have been refused bail.

They are due to appear before a children's court on Monday.

Police are calling for anyone who may have seen anything and are also appealing for information about the identification and location of the three other men.

Australian Associated Press