BALTIMORE, July 2 —Two people were killed and 28 others were injured in a mass shooting in Baltimore, Maryland, early this morning, at the scene of a holiday weekend block party, according to police and local media reports.

An 18-year-old woman and 20-year-old man were killed and three victims were still in critical condition, according to police in Baltimore, a city about 40 miles (64 km) north of Washington, DC.

The suspect or suspects were still at large.

"This investigation is ongoing, and we will not rest until the people responsible are held accountable,” Mayor Brandon Scott and the police department said in a joint statement.

The tragedy rattled the city at the start of the Fourth of July holiday weekend, when Americans typically gather for parades, barbecues and fireworks. The shooting occurred shortly after midnight at the "Brooklyn Day” block party in the Brooklyn Homes neighbourhood of Baltimore, which hundreds of people attended, local media reported.

A witness told TV station Fox 45 that they had heard 20 to 30 shots fired.

A local reporter posted an image to Twitter showing police tape, cups and other litter strewn across a yard that appeared to be the crime scene.

Nine people were transported from the scene to local hospitals, while 20 others affected walked into hospitals in the area, police said.

Medstar Harbor Hospital’s emergency department treated 19 patients this morning, all suffering varying degrees of injury from gunshot wounds after the incident, MedStar Health Baltimore said in an email. All but one patient had been released as of this morning. — Reuters