The owner of a small cabin off Lake Whitehall said he heard laughter in the woods early Sunday night before the entire three-season home lit up in flames."I heard an explosion of a bunch of fireworks," owner Brian Morrison told the Metrowest Daily News. "Within seconds this wall of flames just shot up."Morrison, who lives in a home on Piazza Lane, a long private dirt road off Wood Street, rushed to call 911. The cabin on the property has been unoccupied for a few years."I saw what looked like three kids in the woods," Morrison said. He said a state police dog searched the woods, but did not find anyone.Fire Chief Steve Slaman confirmed Monday morning his department and police are investigating the report of youths in the area. He said firefighters reached the scene shortly after 6:30 Sunday night."It was burned all the way to the ground at that point," Slaman said.All that is left of the cabin is debris, cinder blocks and a stone chimney.Slaman said a "very extensive" brush fire was sparked by the blaze that extended into Whitehall State Park. He said firefighters left around 9:30 p.m. and returned Monday morning to put out hot spots."It is a very long narrow driveway to get in there so we had to use off-road tankers to shuttle in water to put out the brush fire," Slaman said.Crews from Ashland, Westborough, Milford, Upton and Southborough helped Hopkinton firefighters. Department of Conservation and Recreation firefighters also responded to the scene because of the nearby state park, Slaman said.He said the cause of the blaze is still under investigation, with the assistance of Hopkinton Police.Jennifer Mieth, a spokeswoman for the state Fire Marshal's Office, said the department is aware of the fire but is not part of the investigation.Morrison said they bought the cabin to make sure it wasn't torn down and replaced by a bigger home. The cabin, built in the 1930s, has been the target of vandalism and break-ins in the past, he said.On Sunday, he said he was getting into his car when he heard the commotion."I've never seen anything like that," he said of the blaze.Morrison, a former conservation commissioner in town, said he is waiting to hear back from the Fire Department on what kind of cleanup is needed.He said he's glad he spotted the fire as soon as he did."It would have engulfed more of the woods and possibly our house," Morrison said. "Thankfully, no one was hurt and it didn't take out more of Whitehall State Park."