Police in the U.S. city of Baltimore confirmed on Sunday that two people had died in a "mass shooting incident" overnight at an apartment block in the city and three others were in a critical condition.

The city's police department said 30 people had been shot in the incident at 800 block of Gretna Avenue in Baltimore.

An 18-year-old female was pronounced dead at the scene and a 20-year-old male was pronounced dead after being taken to a local hospital, the police said.

Three others were in a critical condition after nine people were transported from the scene to local hospitals, while 20 others affected walked into hospitals in the area, police said.

The police department said that at about 12:35 a.m. on Sunday officers responded to calls of a reported shooting at 800 block of Gretna Court.

Hundreds of people were gathered in the area for an event called "Brooklyn Day," a witness told TV station Fox 45, adding that they had heard 20 to 30 shots fired. (Reporting by Jahnavi Nidumolu and Shivani Tanna in Bengaluru Editing by David Goodman, Simon Cameron-Moore and Susan Fenton)