Two police cars whizzed by Norma Onstad Monday afternoon as she headed toward her daughter's Tonka Bay home to check on some newborn puppies.

Moments later, Onstad learned why the police had been in such a hurry.

She watched in horror as flames shot out of the two-story house on the 100 block of Lakeview Avenue following an explosion. There were five dogs inside.

Miraculously, one of them, a female Labrador retriever, survived, said Scott Gerber, chief of the Excelsior Fire District. Her four puppies died.

No one was injured in the blast, which occurred just before 4 p.m. The homeowners, Scott and Michelle Schmitt, were on their way home Monday afternoon after spending some time at their cabin.

Onstad was on her way to check on the puppies, which were born Friday. "One was not doing very well," she said.

Gerber said officials have not determined the cause of the fire. But relatives at the scene suspect a space heater might have been to blame.

The dog and her litter were being kept in the garage with a space heater to keep them warm.

'More than burning leaves'

The explosion rocked the neighborhood on the west end of Lake Minnetonka, and several neighbors called 911 to report it, including Jamie Erdahl and her sister Jaclyn. They heard a boom and saw billowing smoke.

"It was more than somebody burning a pile of leaves," said Jaclyn.

Within minutes, dozens of firefighters from several agencies arrived on the scene, but not soon enough to save the dogs -- or the structure that the Schmitts had built two years ago.

Gerber said the fire was "very far advanced" by the time crews arrived.

"They put all the sweat equity into it," said Peter Onstad, Michelle's father. "The house is a total loss."

Gerber said the Schmitts were able to retrieve some possessions.

This is not the first time a house at 165 Lakeview Avenue has burned. Norma Onstad said a previous home on the property burned down about 10 or 12 years ago.

Tim Harlow • 651-925-5039