Washington - The details of a shooting spree across three southern Alabama towns began to come to light Wednesday, a day after a gunman killed 10 people, including family members and several apparent strangers, before committing suicide.

Hours after the shootings began on Tuesday it became clear that the attacker, 27-year-old Michael McLendon, had first shot and killed his mother before setting her house on fire in Kinston, Alabama, near the Florida state line, local media reported.

Police said in televised press briefings on Wednesday the rampage was the worst in the southern state's history. A motive for the shootings remained unclear.

He then killed seven people in three homes in the neighbouring town of Samson, including his grandparents, an uncle and aunt, and a neighbour - who was the wife of one of the officers who responded to the shooting - and their young child. An infant was also injured in the attack.

The gunman, who was described as carrying a semiautomatic weapon, is believed to have acted alone, state police said.

After leaving the town, the gunman is reported to have opened fire on an Alabama state policeman on a highway. The officer suffered minor injuries from broken glass, and his squad car was struck by seven bullets.

Two more victims were shot to death along the same highway, one at a business and the second at a petrol filling station.

Outside the nearby town of Geneva, the gunman is suspected of unleashing 30 rounds at a metal manufacturing company with police in pursuit. A Geneva police chief was wounded at the scene.

The suspect entered the small factory, where he was a former employee, and police followed after hearing more gunfire to find the body of the gunman with an apparent self-inflicted bullet wound.

Several additional people were wounded in the shooting spree.