An 18-year-old woman and 20-year-old man were killed and 28 others were injured in a mass shooting in the U.S. city of Baltimore on early Sunday morning after a neighborhood party, police said.

Roughly 14 of the victims were under 18 years old, acting Baltimore Police Commissioner Richard Worley said in a news conference.

Police were still looking for suspects and said the motive remains unclear.

Baltimore Mayor Brandon Scott urged people with information to come forward to assist investigators locate the "cowards" who were responsible for the shooting.

"We will not stop until we find you, and we will find you. Until then, I hope that every single breath you take, that you think about the lives that you took, think about the lives that you impacted here tonight."

Local resident Terry Brown told the Baltimore Sun he was standing outside his home when he heard the crackle of gunfire, followed by a stampede of people fleeing in panic for cover.

"It was chaos," Brown said. "Parents were running around looking for their children, hollering and screaming, and don't know if their child has a bullet in them."

"Maryland has had enough of watching gun violence continue to ravage our state and our nation," Maryland Governor Wes Moore said in a statement. "The fact that these horrific shootings continue to take place is abominable. We as a state will continue to do everything we can to prevent senseless acts of violence like the one we saw last night."

The U.S. witnessed 338 mass shootings, defined as an incident where four or more people are killed or injured, so far this year, according to the Gun Violence Archive.

(With input from agencies)

(Cover: A police officer moves a scooter in the area of a mass shooting incident in the Southern District of Baltimore, Maryland, U.S., July 2, 2023. /CFP)