(CNN) -- Eight people died early Monday in Buenos Aires, Argentina, when a city bus and a police ambulance collided, the government news agency reported.
The dead included three police officers and one of two female occupants of the ambulance, the government-run Telam news agency said.
The other fatalities were pedestrians, at least some of whom were believed to have been homeless people living on the street.
The accident happened around 12:30 a.m. in the Argentine capital.
At least six people also were injured, said firefighter Fernando Malaf. All were expected to recover.
No official cause for the accident was immediately given. But witnesses told police the ambulance, which had its siren on, went through a red light and hit the bus on the driver's side, Telam said. The impact spun the bus around so it ended up facing in the opposite direction.
Both drivers were reported injured.
A tree was knocked over and two cars also were involved in the chain-reaction accident.
The crash occurred in front of a city park. Federal police spokesman Tomas Vigliatore said officials did not know what the people who were injured or killed were doing in the area. But witnesses and a fire department spokesman said at least some of them were indigents living on the street.
One of the female passengers in the ambulance had suffered a heart attack and the other woman was accompanying the patient, Telam said. The cardiac patient died in the crash, the news agency said.