The emergency services were first alerted to the explosion at about 20:30 on Sunday (11:30 GMT).

Japanese broadcaster NHK said the area affected had both residential and dining establishments and was about 3km south-east of the city centre. 

The Japan Times carried an image of firefighters working at a collapsed building and quoted one eyewitness as saying the explosion sounded like thunder.

Another eyewitness told NHK that the blast had broken the windows of the restaurant he was working in, and that there were "many injured people".

Image copyrightEPA

Image captionThe emergency services were first alerted to the explosion at about 20:30 local time on Sunday