At least 15 people died and 18 were injured on Wednesday when Lisbon’s Gloria funicular railway car, which is popular with tourists and is one of the city’s symbols, derailed and crashed, an emergency medical service spokesperson told reporters.

Authorities did not identify the victims or disclose their nationalities, but said some foreign nationals were among the dead. Five people were gravely injured, the spokesperson said.

“It’s a tragic day for our city. … Lisbon is in mourning, it is a tragic, tragic incident,” Carlos Moedas, mayor of the Portuguese capital, told reporters.

Portugal’s government declared a day of national mourning on Thursday.

Footage from the site showed the destroyed yellow tram-like funicular, which carries people up and down a steep hillside in the Portuguese capital. Emergency workers were pulling people out of the wreckage.

President Marcelo Rebelo de Sousa lamented the tragic accident in a statement, expressing hope that authorities would soon establish what had caused the crash.

Police investigators were inspecting the site and the prosecutor general’s office said it would open a formal investigation, as is customary in public transport accidents.

The line, which opened in 1885, connects Lisbon’s downtown area near the Restauradores Square with the Bairro Alto (Upper Quarter), famous for its vibrant nightlife.

It is one of three funicular lines operated by the municipal public transport company Carris and is used by tourists as well as local residents.

Carris said in a statement that “all maintenance protocols have been carried out”, including monthly and weekly maintenance programs and daily inspections.

The Gloria line transports around 3 million people annually, according to the town hall.

Its two cars, each capable of carrying around 40 people, are attached to opposite ends of a haulage cable with traction provided by electric motors on the two cars.

The car at the bottom of the line was apparently undamaged, but video from bystanders aired by CNN Portugal showed it jolting violently when the other one derailed and several passengers jumping out of its windows and people shouting.

Portugal, and Lisbon in particular, has experienced a tourism boom in the past decade, with visitors cramming the popular downtown area in the summer months.

A spokesperson for Britain’s Foreign, Commonwealth and Development Office said it was in touch with the local authorities and stood by “to provide consular assistance if there are any affected British nationals”.

Britain is the largest source of tourism to Portugal, followed by Germany, Spain and the United States. The U.S. State Department did not immediately respond to a request for comment.