A gunman wearing body armour and a mask opened fire in a crowded Dayton, Ohio neighborhood known for its night life early on Sunday, killing nine people including his sister and wounding at least 27, authorities said, in the second deadly US mass shooting in less than a day.

Police named the gunman as Connor Betts, a 24-year-old white male from Bellbrook, Ohio, and said he was armed with an assault-style rifle fitted with an extended drum magazine that could hold 100 rounds.

His sister Megan Betts, 22, was one of the first victims to be killed. Biehl said the siblings had arrived in the same vehicle with a third companion earlier in the evening, but separated before the rampage.The companion was wounded in the shooting, police said.

Police officers on routine patrol nearby were on the scene in less than a minute and shot the attacker dead moments after he opened fire, likely preventing a much higher casualty toll, authorities said.

Biehl told reporters the bloodshed began at 1 a.m. local time in the city’s Oregon District, an historic neighborhood popular for its nightclubs, restaurants, art galleries and shops.

Video recorded outside the Ned Peppers Bar showed revelers enjoying a summer night and then suddenly having to flee for their lives as shots rang out and officers raced to the scene and opened fire on the suspect.

Many ran into the tavern to try to escape the gunman’s bullets, the police chief said.“Had this individual made it through the doorway of Ned Peppers with that level of weaponry, there would have been catastrophic injuries and a loss of life,” Biehl said.