Two police officers and several firefighters were injured in an explosion at an apartment building in the western German town of Ratingen on Thursday, said the state interior ministry.
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Police and firefighters were called to aid a helpless person and, when they arrived, there was an explosion at the door to the apartment, said a police spokesperson.
It was unclear what caused the explosion, said police and the interior ministry for the state of North Rhine-Westphalia.
A large-scale police operation was underway, the ministry said.
Broadcaster ZDF reported that 10 firefighters and 2 police officers had been injured, and security sources could not rule out a targeted attack.
At around 0800 GMT, the apartment owners' association notified police that the mailbox of one of the residents was overflowing, ZDF reported, citing the state interior minister.
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Police then called in firefighters to open the door to the flat where a mother and her son were living, and there was a fire in the room, the broadcaster reported.
{{/usCountry}}Police then called in firefighters to open the door to the flat where a mother and her son were living, and there was a fire in the room, the broadcaster reported.
{{/usCountry}}Interior Minister Nancy Faeser was set to make a statement on the incident in the afternoon, ZDF said.