BALTIMORE (AP) — Gunfire erupted at a block party in Baltimore on Sunday — killing two people, wounding 28 and leaving an extensive crime scene that marred the U.S. holiday weekend, police said. Three of the wounded were in critical condition.

Baltimore Police Department Acting Commissioner Richard Worley told reporters there were a total of 30 victims during a press conference at the scene.

The shooting took place just after 12:30 a.m. at a block party in the Brooklyn Homes area in the southern part of the city, Worley said.

The shooting comes amid gatherings around the country leading up to the July Fourth holiday. Elsewhere, a shooting in Kansas left seven people with gunshot wounds and two more victims hospitalized after being trampled as people rushed out of a nightclub early Sunday morning, police there said.

Nine victims were transported by ambulance and 20 victims walked into area hospitals with injuries from the shooting, Worley said.

Nineteen of those victims were treated in the emergency department at MedStar Harbor Hospital, according to hospital spokesperson Debra Schindler. Nine of the critically injured patients were stabilized and transferred to Baltimore trauma centers. All but one of the 19 victims sent to MedStar have been released.

“As is protocol following any walk-in victim of violence, the hospital went on immediate lock-down to secure the campus and ensure the safety of all patients and associates,” Schindler said in a statement. “Multiple critically injured patients were evaluated and triaged simultaneously by clinical staff, while hospital security managed the throng of family members that gathered in and outside of the emergency department.”

Meanwhile, dozen victims were sent to be treated at R Adams Cowley Shock Trauma Center and four others were sent to the University of Maryland Medical Center’s Pediatric Emergency Department, according to University of Maryland Medical System spokesman Michael Schwartzberg.

An 18-year-old woman was found dead at the scene and a 20-year-old man was pronounced dead at a hospital shortly after, police said.

“I want those who are responsible to hear me, and hear me very clearly,” Mayor Brandon Scott said at the scene. “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.”

No arrests were made immediately after the shooting. Scott asked anyone with information to come forward to assist investigators locate the “cowards” who were responsible for the shooting.

Authorities said the crime scene was extensive and that it will take some time for detectives to work it.

“Treat this as if it were your family,” Scott said. “How you would want people to treat it if you were mourning, if this was your neighborhood, if this was an event in your community that this happened at. We want you to treat it that way because that’s how we have to treat each other as Baltimoreans.”

Hours after the shooting, a number of officers remained on the scene, working behind police tape amid densely packed two-story housing blocks. Folding tables and plastic cups were scattered around the scene, apparently left behind when people ran from the gunshots.

Lakell Nelson said there had been several false alarms of people mistaking the sounds of fireworks for gunfire earlier in the night while she was at the block party. However, by the time she was getting to her car, the actual shooting began.

“The shots were just going on and on and on,” she said.

That’s when two young women approached her and said they’d been shot, with one woman showing how a bullet had gone through her shorts.

Nelson said told the women to get in the car and she sped through red lights to get to the nearest hospital.

“When I pulled up to the door of the hospital, my car was almost getting ready to be inside the hospital, because I was determined to get those babies in that hospital,” Nelson said.

The violence comes as federal prosecutors in Baltimore this week touted their efforts to reduce violent crime in the city. Police have reported nearly 130 homicides and close to 300 shootings so far this year, though that’s down from the same time last year. Authorities have vowed to crack down aggressively on repeat violent offenders.