Four people were killed and 15 were injured in three shootings in Dallas's Deep Ellum district early Sunday, police said. Deep Ellum is an entertainment district with shops and restaurants, AP reported.

The department's November 1 statement identifies scenes in the 2600 blocks of Elm and Main streets and the 200 block of South Crowdus Street. Its timeline runs from about 12:20 a.m. to 1:35 a.m. No officers were injured.

Chief Daniel Comeaux said investigators were still working to establish whether the shootings were connected, the Associated Press reported. He said some people had been arrested and were being interviewed, without identifying charges or explaining their connections to each scene.

Several injured people reached hospitals on their own, FOX 4 reported from the chief's briefing. Comeaux described the injury toll as approximate while investigators gathered information from hospitals.

Officers had increased patrols for Halloween crowds, FOX 4 reported. Detectives planned to canvass nearby businesses for surveillance footage and review area cameras. Police also asked people with photographs, video or social media clips from the area to come forward.

Anyone with information can contact Sgt. Boz Rojas at 214-671-3598 or [email protected], the department said. Its statement lists three separate case numbers for the investigation.