An explosion was heard on Friday at Shimizuzaka Park in Kita Ward, northern Tokyo, Japan.
Police are investigating after receiving reports of the incident around 5:15 p.m. local time (0815GMT) that an object left behind by a man was detonated, the Metropolitan Police Department said in a statement.
Around 20 police officers, including forensic investigators, were deployed to the scene to examine the area.
No injuries have been confirmed, the police said.
The police are currently working to identify the detonated object and reviewing security camera footage to collect more information about the incident.
Law enforcement cordoned off the park, which is located in a residential area about one kilometer south of JR Akabane Station, as they launched an investigation.
