Updated: Officials in a Philadelphia suburb have yet to capture an Iraq war veteran they say went on a shooting rampage early on Monday that left six of his estranged family members dead, including his ex-wife and her 14-year-old niece.

He also apparently briefly abducted his two daughters from his ex-wife's home before dropping them off with a neighbour and vanishing.

Former Marine Corps Sergeant Bradley William Stone, 35, of Pennsburg, Pennsylvania, is being sought for shootings at homes in the towns of Lansdale, Lower Salford Township and Souderton near Philadelphia.

Neighbours in Souderton, Pennsylvania, where suspect was believed to have been barricaded inside after shootings at multiple homes.

Law enforcement officials described a series of attacks between 3.30am and 5am, after Mr Stone dropped off his daughters and disappeared, abandoning his vehicle and his cellphone at an undisclosed location.

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The victims were all family members of Stone's ex-wife, Nicole, 33, who divorced Stone in 2009 and was found dead in her home in Lower Salford Township.

"They've been fighting for years, real bad," a neighbour, Michele Brewster, told the Allentown Morning Call of Nicole and Bradley Stone. "He's been tormenting her. She's gone to the police, and she has told everybody, 'He's going to kill me.'"

Police move near the scene of one of the shootings.

The pair had been involved in a protracted custody battle over the pair's two daughters, Matthew Schafte, 42, a friend of Bradley Stone's, told the Los Angeles Times.

"She was trying to hold the kids from him, and he just snapped," guessed Mr Schafte, of Harleysville, who said he's known Mr Stone for 20 years. "But to snap by killing her family members is not the Brad that I know. ... He was a nice guy."

Mr Stone was seen about 5am, after the rampage, when he "delivered" the two daughters to a neighbour in Pennsburg, in eastern Pennsylvania's Montgomery County District Attorney Risa Vetri Ferman told reporters in a brief news conference.

The girls were safe, Ms Ferman said. But several members of their extended family are dead.

The first attack apparently began at 3.30am in Souderton, where Nicole Stone's sister, Patricia Flick, Flick's husband, and the pair's 14-year-old daughter were found dead, Ms Ferman said.

Flick's 17-year-old son was injured in the attack and was apparently not found until shortly before 8am, when authorities visited the home and transported him to an area hospital, Ms Ferman said. His name was not released and the extent of his injuries is not known.

Nicole Stone's mother and grandmother were also found dead at a home in Lansdale after a hang-up 911 call was placed to police at 4.25am, Ms Ferman said. Officials did not give their names.

Nicole Stone was found dead after a police call from a neighbour at 4.55am, Ms Ferman said.

"I heard a 'pow', and I thought, 'Was that a gun?'" Ms Brewster, Nicole Stone's neighbour, told local media. Another neighbour, Ashley Deane, told a local newspaper she heard what sounded like four gunshots and could hear children screaming for their mother.

Ms Deane said she could hear her neighbour's ex-husband telling the children that they had to leave. She said she looked out the front window and she could see him with the children, ages 5 and 7, who were in their pyjamas.

Bradley Stone had looked at Ms Deane and said, "She's hurt," referring to his ex-wife, Ms Deane added that the ex-husband and the children then got in a car and sped off.

The ensuing manhunt forced local schools to shelter in place as authorities spent the day hunting for the balding, red-haired Bradley Stone, whom officials consider armed and dangerous. Local media reported that SWAT teams swarmed his home in Pennsburg, apparently with no result.

A Facebook page under Mr Stone's name said he had a son and showed a photo of him kissing the bride at a wedding. Among favourite quotes listed on the Facebook page: "If you [expletive] with me, I'll kill you all," and "Be polite, be professional, but have a plan to kill everyone you meet".

Mr Stone's friend, Mr Schafte, described his interests as being focused on Marines and on his children, which now included a son with his most recent wife.

"He loved life, he loved his country, he went to serve, he was so proud of his babies, especially when he got married to Nicole," Mr Schafte said, adding that around town "he'd be a bartender or help out or go to the local legion or VFW [ Veterans of Foreign Wars of the United States] - it was all about veterans."

The Marine Corps confirmed Mr Stone's service, and said he enlisted as a reservist in 2002 and left duty in 2008, remaining on individual ready reserve in case of a call-up until 2011.

Mr Stone served in Iraq from April 17, 2008, to July 2, 2008, the only deployment on his record, according to a spokeswoman for the Marines.

TNS