An explosion at a building in Tokyo’s Shimbashi commercial district shattered windows and spewed smoke, injuring four people, officials said.

The Tokyo Fire Department said the explosion occurred at a restaurant on the second floor of an eight-storey building, injuring two people inside and two pedestrians who were hit by shards of glass.

The four injured were all conscious but further details were unknown, fire officials said. NHK national television said three of them were seriously injured.

An owner of the restaurant, who was among the injured, told police that he noticed a smell of gas or sewage when he entered a smoking room, and the explosion occurred when he flicked his lighter, NHK said.