The derailment of a popular streetcar Wednesday in Portugal's capital killed 15 people and injured 18 others, emergency services said, in what officials are calling one of the Lisbon's worst tragedies in recent memory.

Here is what to know about the derailment:

Investigation underway

Official details about the crash were scant Wednesday evening. Authorities called the derailment an accident, and the government said an investigation into the causes would begin once the rescue operation is over.

Eyewitnesses told local media that the streetcar appeared out of control as it careened down the hill at around 6 p.m. during the evening rush hour. One witness said the streetcar toppled onto a man on a sidewalk.

The sides and top of the yellow-and-white streetcar, known as Elevador da Gloria,

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