(CNN) -- A house explosion in a northern suburb of Milwaukee on Saturday injured six people, including a firefighter and a police officer, fire officials said.
The cause of the blast was not immediately clear, but is under investigation, said Kerry Wenzel, a spokeswoman with the North Shore Fire Department.
Video from CNN affiliate WISN showed a gaping hole where a house once stood, as firefighters doused the debris with water.
Fire Chief Robert Whitaker said three structures were involved in the incident -- the house that was destroyed and those on either side of it.
Among the injured were two residents, a neighbor and a passerby, both of whom tried to assist those inside, he said.
The injured police officer was treated for smoke inhalation, while the firefighter was treated for heat exhaustion, the chief said.
CNN's Greg Morrison contributed to this report.