An explosion hit a building in Tokyo's commercial district of Shimbashi on Monday shattering windows and spewing smoke, according to media reports.
Police were investigating the site after receiving an emergency call, Kyodo news reported. NHK television, quoting fire department officials, said four people were injured.
No other information, including the cause, was yet available.
"The sound was deafening. It was as if something huge was dropped from the top of the building -- it was an incredible bang," a male eyewitness told public broadcaster NHK.
(This is a developing story. More details are awaited.)
