LISBON -- Six people died after a car crashed and caught fire early Sunday on Avenida das Forcas Armadas in the north-central area of Lisbon, according to the Public Security Police (PSP).

Authorities said the victims were three women and three men, though their exact ages have not yet been confirmed. Identification documents found at the scene suggest that some of the victims were young adults.

The causes of the accident remain unclear. The Judiciary Police has opened an investigation. The crash took place only a few metres from the United States Embassy, and authorities are working to rule out any criminal involvement.

According to local media, the first person to notice the crash was a PSP officer assigned to security at the United States Embassy. The officer reportedly saw the BMW strike a curb and be propelled several metres forward. He attempted to reach the occupants, but the vehicle burst into flames before he could assist.

Firefighters were alerted at around 3:40 a.m. and arrived within minutes. Due to the condition of the car and the victims inside, emergency responders were initially unable to confirm the number of people involved. Lisbon Metropolitan Command later confirmed that six people had been in the vehicle, which was designed for five passengers, indicating that it was overloaded.