A powerful explosion caused by a natural gas leak killed at least 18 people, including a pregnant woman and a child, and injured dozens Friday when it blew away the outer walls of a luxury hotel in the heart of Cuba’s capital.

No tourists were staying at Havana’s 96-room Hotel Saratoga because it was undergoing renovations, Havana Gov. Reinaldo García Zapata told the Communist Party newspaper Granma.

“It’s not a bomb or an attack. It is a tragic accident,” President Miguel Díaz-Canel, who visited the site, said in a tweet.

Díaz-Canel told reporters that 50 adults and 14 children were hospitalized after the blast and that families in buildings near the hotel affected by the explosion had been transferred to safer locations.

Cuban state TV reported that the blast was caused by a truck that had been supplying natural gas to the hotel, but did not provide details on how the gas ignited.

The blast sent smoke billowing into the air around the hotel with people on the street staring in awe, one saying “Oh my God,” and cars honking their horns as they sped away from the scene, the video showed. It happened as Cuba is struggling to revive its key tourism sector which was devastated by the coronavirus pandemic.

Cuba’s national health minister, José Ángel Portal, said the number of injured could rise as the search continues for people who may be trapped in the rubble of the 19th-century structure in the Old Havana neighborhood of the city.

“We are still looking for a large group of people who may be under the rubble,” Lt. Col. Noel Silva of the Fire Department said.

An elementary school next to the hotel was evacuated. It was not immediately clear if the injured children were students.