A mother has been shot dead and her five-year-old son hit by a bullet in a limb during a gunfight with police over traffic offences. Korryn Gaines, 23, allegedly threatened police with a gun during the altercation, which occurred at Gaines' home in Baltimore County, Maryland, on 2 August.

Gaines had allegedly barricaded herself in her home and gunfire was exchanged with Baltimore Police, who said they were as yet unclear about whether the woman's five-year-old son had been hit by a bullet fired by police or his mother.

He was taken to hospital with non-life threatening injuries and is expected to make a full recovery.

"We are of course extremely upset at an event like this," police spokeswoman Elise Armacost said at a press conference. "We do not like to be in a position of having to use lethal force, but this was a situation where our officers exercised patience for hours and hours. We are very relieved the child was not seriously injured."

The standoff began after three officers arrived at Gaines' property with an arrest warrant for her and a man who has not been named. Gaines was wanted in connection with several traffic offences and an unfulfilled court appearance, also related to traffic offences.

When the police initially knocked at the property, they said they could hear voices but no one answered, prompting them to get a key from the landlord and open the door.

One of the officers said he opened the door to find a woman sitting on the floor pointing a "long gun" at him, stating he left the apartment and called for backup.

A man ran from the apartment with a one-year-old child, but the woman and her five-year-old son remained in the apartment during what police described as a "barricade situation" that began at around 9.40am and lasted into the afternoon. Residents were evacuated from the building.

At around 3pm officers allege the woman opened the door and said, "I'm going to kill you". At this point a shot was fired at her. She returned fire and the officers fired again, leaving the woman with fatal wounds. No officers were hit during the altercation and police said it was unclear whether the officers involved were wearing body cameras.

The group Black Lives Matter has shared a number of posts about the young mother, with a vigil for Gaines planned for 7pm on 5 August at Baltimore College.