Three people are dead and four more were hospitalized after police responded to multiple 911 calls early Sunday in Pittsburgh's trendy South Side Flats area, authorities said.

The initial investigation suggested drug-related overdoses, raising concerns that a tainted, deadly batch of drugs could still be circulating in the community, police spokesman Chris Togneri said.

The victims apparently were attending an event together before going to a private residence, Togneri said in a statement. The victims, all men, were wearing orange wristbands apparently distributed by a venue in the city. The victims later took the narcotics at about the same time, he said.

"To be clear, this was not a case of a tainted drug being passed around or distributed in large volume at a large venue, which could have affected even more people," Togneri said. "It appears to have been isolated to a single location."

Still, police remained concerned that more deadly drugs could surface.

"We remind the public not to use drugs. Simply put: You do not know what's in that drug," Togneri said.

Police identified multiple venues in the city that used orange wristbands Saturday night for events and concerts. The event that linked the men had not been determined Sunday, but police said that anyone who attended any of the events has no cause for concern.

Five of the victims were found in an apartment, one was in an elevator outside the apartment and one on a nearby street, police said. Those hospitalized were in conditions ranging from critical to serious, police said.

Police earlier had confirmed "multiple hospitalizations and deaths" after responding to a "medical situation" early Sunday.

The incident began about 2 a.m. with a 911 call for an unresponsive man in an apartment building, Pittsburgh Director of Public Safety Wendell Hissrich told the Pittsburgh Tribune-Review. A short time later, another man found semiconscious on a nearby street was traced to the same building, where police then found five more victims.

Pittsburgh EMS found no air-quality issues that could endanger the building's other residents, Hissrich said.

In a statement released to the Pittsburgh Post-Gazette, the South Side City Club Apartments said the victims didn't live there.

“These were acquaintances of a good standing resident, who apparently was not in the apartment at the time the individuals were found," the statement said. “It is our understanding that the group had attended an outside event where they may have consumed a toxic substance before returning to the apartment.”

The South Side Flats area includes a bevy of bars, restaurants and eclectic stores. East Carson Street, where the person on the street was found, runs through the heart of the district.

The investigation was continuing.