NEW YORK (CBSNewYork) – A carbon monoxide explosion and an electrical fire on the same block caused dozens of Upper West Side apartments and businesses to be evacuated Sunday.

Windows at Equinox on Broadway were blown out. Shattered glass covered the street after the frightening carbon monoxide explosion.

“Look like a bomb blast,” Mahendra Patel told CBS2’s Hazel Sanchez.

Patel was working at a bodega across the street when he heard the blast around 6:30 p.m.

Firefighters were already at the scene for three hours, responding to a call for an electrical fire inside the gym.

A malfunctioning underground Con Edison transformer right outside the building was smoldering, smoke and gas spread into the basement of Equinox.

Firefighters detected high levels of carbon monoxide and immediately created a safe zone on Broadway between 91st and 92nd Streets and evacuated 90 people inside the gym, neighboring businesses, and a nearby bank.

“Gas is a very dangerous substance and any short caused by many things – as little as a telephone ringing or a light switch been turned on – can trigger an explosion,” FDNY Asst. Chief John Hodgens explained.

Remarkably, no one was hurt, including the animals in a nearby Petco.

Gas and electricity was shut off on the block while fire crews ventilated the buildings and checked co levels.

Con Edison is still trying to determine what caused the transformer to malfunction.