An abandoned building engulfed in flames in downtown Sao Paulo collapsed Tuesday as firefighters worked to put out the fire that began in the wee hours of the morning.

Firefighters said at least one person was killed in the collapse and that there could be more victims. Officials said the inferno began at around 1:30 a.m. and it wasn’t known how many people were inside.

At least 160 firefighters rushed to the scene, The New York Times reported.

A few hours after the fire started, the 20-story building collapsed. Footage of the collapse showed the multi-story building falling on itself as the blaze raged. Debris could be seen falling into the surrounding streets.

Romulo de Souza, 49, was part of a squatter occupation in the neighboring building and said that when the fire started on the fourth floor of high rise, people started to evacuate his building.

"Happily the majority got out," he said, adding that residents believed the blaze could have been started by a gas leak.

The building was formally a headquarters for federal police but had been abandoned for many years and had been occupied by squatters, according to local media.

Officials expected to find victims, but didn’t know how many, firefighter Lt. Andre Elias told Globo TV.

The Associated Press contributed to this report.