A US former Marine and Iraq war veteran suspected of killing six people, including his ex-wife, in Philadelphia has reportedly been found dead.

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, a prosecutor says.

Six people are dead and one has been wounded in shootings in several homes and the suspect remains on the loose, officials in the US say.