POLICE hunting a man suspected of going to three houses and shooting dead six people, including his ex-wife and her 14-year-old niece, do not know where he is or how he is getting around.

Officers recovered the phone and car of Iraq war veteran Bradley Stone, who had recently been in court fighting with his ex-wife over custody of their two children.

Elite police teams surrounded his home in Pennsburg, Pennsylvania, a suburb of Philadelphia, and pleaded through a loudspeaker for him to surrender, but Montgomery County district attorney Risa Ferman said it was unclear if he was there.

She said: "As I stand here right now, we do not know where he is."

The shooting rampage started at the home of Mr Stone's former sister-in-law in Souderton and ended about 90 minutes later at ex-wife Nicole Stone's apartment in nearby Harleysville, Ms Ferman said.

Ms Stone's sister Patricia Flick, her husband Aaron and the couple's 14-year-old daughter Nina were killed in the first wave of violence.

Their 17-year-old son Anthony was pulled from the home with a head wound and taken in an armoured vehicle and then by helicopter to a Philadelphia hospital.

Ms Stone's mother Joanne Hill and grandmother Patricia Hill were killed next at their home in nearby Lansdale. Investigators were alerted by a hang-up call to emergency dispatchers.

Ms Stone's neighbours at the Pheasant Run Apartments in Harleysville said they were woken by the sounds of breaking glass and gunshots coming from her apartment. They said they saw Mr Stone fleeing with their two children and alerted authorities.

"She would tell anybody who would listen that he was going to kill her and that she was really afraid for her life," neighbour Evan Weron said.

The two children Mr Stone took from his ex-wife's house were safe, Ms Ferman said. She did not say what weapon or weapons were used.

Several school districts ordered pupils and teachers to shelter in place.

Brad and Nicole Stone married in 2004 and filed for divorce in March 2009, according to court records.

Brad Stone, 35, remarried last year, according to records. Nicole Stone, 33, became engaged over the summer, neighbours said.

The former had couple sparred over custody of their two children, with Brad Stone filing an emergency petition on December 5 and Nicole Stone responding with a counter-claim on December 9. The outcome of their dispute was unclear.

Ms Weron said Stone was a military veteran. He was a barman at the American Legion hall in Lansdale and court records show he recently faced several drink-driving charges, one of which was handled in veterans' court.