Four people were injured after an explosion in a building in Tokyo’s Shimbashi district on Monday, the Tokyo Fire Department said, with glass and debris scattered around the scene as smoke rose from the second floor.

A fire following the explosion was later extinguished, and the injured were taken to a hospital. The blast, which originated in a bar on the second floor of the building, was reported at about 3:15 p.m.

The bar’s manager said he had tried to light a cigarette in a smoking area of the establishment when the explosion took place, according to the police. The site was said to be filled with gas, with investigators working to confirm further details.

Two of the injured were employees of the second-floor bar, with the other two passersby, the fire department said.

“I was working on tasks that didn’t involve fire, like cutting vegetables and prepping the store, when I felt a strong shock coming from the floor above,” said Shinobu Nakagawa, 25, a staff member at the restaurant on the first floor of the building, who was alone at the time.

He said he had picked up a faint smell of gas on his way to the store at around 2:30 p.m. but realized the smell had grown stronger once he entered the building. Nakagawa believes the explosion happened shortly before 3 p.m.

The eight-story building, located west of JR Shimbashi station, is home to a restaurant called Torisuta on the first floor, a bar on the second floor, and clinics on the third and fourth floors.

The second floor bar was closed at the time of the explosion.