WELLS — Maine officials have ruled that an intense fire on Sunday that leveled an oceanfront home on Wells Beach was accidental.

The blaze, which produced plumes of heavy black smoke that could be seen for miles, started late Sunday afternoon after a propane leak and explosion at the three-story home at 149 Atlantic Ave., according to the Office of the State Fire Marshal.

Investigators from the state fire marshal’s office determined that a resident of the home had just changed a propane tank and was preparing to grill when a fire erupted nearby, causing a small explosion. That led to leaking propane and four small explosions on the lower level of the home, the Wells Fire Department said.

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Before the homeowner could grab a fire extinguisher, the fire spread rapidly, destroying the home and causing damage to two neighboring houses from heat and fire exposure.

The homeowner was treated at the scene for minor burns; his daughter, who was also in the area at the time, was not injured.

The Wells Fire Department arrived on the scene and ultimately declared it a four-alarm fire, meaning crews needed support from surrounding departments to suppress the blaze, according to the fire marshal’s office.

Wells Assistant Fire Chief Jonathan Gay said in a news release Monday afternoon that 14 different fire departments helped with the response, including crews from Somersworth, New Hampshire.

On Monday, motorists along Atlantic Avenue — which had closed Sunday during the response to the fire — slowed to a crawl while passing the scene. A handful of passersby stopped to snap photos, with some saying they were at a loss for words.

Sue Larsen, a summer resident of Wells, said she realized something was wrong when she saw the plume of black smoke from her window down the street near the Seaside Cottages.

“All of a sudden, I saw the huge cloud of black smoke floating north,” she said. “It was terrible.”

Jan Spirito, who owns a condo nearby, said the fire burned for at least three or four hours.

“It was quite scary,” she said Monday, looking up at the remains of the house from the beach. “I stayed indoors because I knew it would be dangerous to be out there with all that smoke.”

Spirito also shared her concern for the homeowners, including the two on either side who had also been impacted.

“I just feel so bad,” she said.

Both women credited first responders who arrived on the scene, saying they had done great work extinguishing the flames.