An electric streetcar that is one of Lisbon’s landmarks and a big draw for tourists derailed Wednesday, killing 15 people and injuring 18 others, emergency services said.

Five of the injured are in serious condition, and a child is among the injured, the National Institute for Medical Emergencies said in a statement. An unknown number of the injured are foreigners, it said.

Authorities called it an accident, the worst in the city’s recent history, and it cast a pall over Lisbon’s charm for the millions of foreign tourists who arrive every year.

The yellow-and-white streetcar, which goes up and down a steep downtown hill in tandem with one going the opposite way, was lying on its side on the narrow road that it travels along.

Its sides and top were partially crumpled, and it appeared to have crashed into a building where the road bends. Several dozen emergency workers were at the scene but most stood down after about two hours.

Eyewitnesses told local media that the streetcar careened down the hill, apparently out of control. Carris, the company that operates the streetcar, said scheduled maintenance had been carried out.

Portugal’s government announced that a day of national mourning would be observed on Thursday.