FORT WAYNE, Indiana (AP) - A man pulled a woman off a city bus on Wednesday, fatally shot her and then took a three-year-old boy hostage before a sniper killed him during a police stand-off.

A police officer carried the child out of a house in Fort Wayne, Indiana, about 4.30pm local time (4.30am Singapore time) and police announced soon after that the suspect, 45-year-old Kenneth Knight, was dead.

Police said from the outset that they did not believe the shooting was random, but the relationship, if any, between Knight, the woman and the child was not immediately clear.

Police spokesman Raquel Foster said a protective order had been filed against Knight in the past few days, but she did not say who had requested the order.

Police said Knight and the woman, 49-year-old Jacqueline Bouvier Hardy, had both been riding a city bus when Knight pulled her off and shot her about eight metres away in front of several people.

The shooting took place about 8am along a busy street. Children waiting at school bus stops were among the witnesses, a school official said.

A backpack lay at the feet of the victim, whose body was covered by a sheet.

Knight fled after the shooting into the surrounding neighbourhood. Several hours later, police said a stand-off had ensued and the child was being held hostage.

A few hours later, Police Chief Rusty York told reporters Knight was dead, killed by a single shot from a sniper.