MIDDLETON, Wis. — Two people died when a house exploded in southern Wisconsin and authorities believe gunfire reported by neighbors happened when flames set off ammunition stored inside the home, police said.

Sheriff's deputies and firefighters responded at about 11 p.m. Tuesday, after the house exploded just outside the city of Middleton, said Elise Schaffer, a spokesperson for the Dane County Sheriff's Office.

Police originally found that one person was killed. Later on Wednesday, police found a second person who had died at the scene of the explosion, said Middleton Fire Chief Aaron Harris. The county medical examiner's office is investigating, Schaffer said Wednesday.

Dane County Medical Examiner’s Office confirmed the two deceased people to be Rudolf N. Niederhauser, 82, and Ursula "Uschi" Niederhauser, 82. They were pronounced dead at the scene. 

No additional people were at the home, but Harris said a dog that survived the explosion was found alive, checked out at an emergency veterinary clinic and determined to be in good shape.

Images posted by local media show the ruined home in flames after the explosion, which left a window and other debris scattered nearby.

The sheriff's office said in a news release that the fire “may have set off ammunition inside the home,” leading some nearby residents to report the sound of gunfire. 

“The house was down immediately following the explosion and there was a large debris field,” Harris said. “There was a very large fire following the explosion.”

The cause of the explosion remains under investigation, Schaffer said. Harris said the home that exploded is in a rural area nearly 4 miles north of downtown Middleton. That city is about 6 miles northwest of Madison.

Schaffer said she had no additional information to release as of Wednesday morning.