MADRID (AP) — An explosion ripped through a four-story residential building in central Madrid on Friday, killing two people and injuring at least 18 others, authorities said.

Spanish emergency services initially said they were searching for two missing workers doing work on the building. After an hours-long search, firefighters said the bodies of two people, ages 21 and 27, had been found amid the rubble.

Video released by the city of Madrid showed paramedics attending to the injured at the scene in the upmarket neighborhood of Salamanca, as police and firefighters cordoned off streets that were cluttered with glass and debris.

Four of the injured were taken to a hospital, including one person in serious condition, after the blast sent plumes of smoke billowing into the air. Emergency crews combed the building to check the structure and to search for anyone trapped inside, Madrid Mayor José Luis Martínez-Almeida told broadcaster Telemadrid.

Asked about reports that a gas leak had caused the explosion, the mayor said it was too early to know.

“Some work was being done in the building and neighbors said there was a powerful explosion,” he said.

Spanish Prime Minister Pedro Sánchez said in a tweet that his office was closely following the situation and offered his support to the victims.