One neighbor got up three times to check on what he also thought were gunshots.
"A few minutes later I heard it again. Came back to the window and looked and flames were shooting out through the roof," said Adolph Zoellin.
Fire officials says the popping sounds may have come from acetylene tanks stored inside the barn.
About a hundred firefighters from ten companies fought to bring the blaze under control. Before they arrived on scene some neighbors approached the blazing barn to try to save some of the animals.
"Tried to go 'round to get to where the pigs were and I couldn't get close. It was too hot, you couldn't get near it," said neighbor Leroy Hersteine.
The farm is owned by Greg Kruz, president of Lampire Biological Laboratories, a global firm that supplies animal blood products and other items to the pharmaceutical and biological testing industry. Neither Kruz nor anyone from the company would speak with reporters at the scene.
Throughout the day firefighters have been hosing down wet spots while huge claws removed 3000 bales of burning hay that had just been stacked in the barn in the last week.
"We're in the process of moving those bales out into another field where they can be wet down to keep them from rekindling," said Ottsville Fire Company chief Doug Skelton.
The Bucks County Fire Marshal says the cause of the fire at this point is undetermined, but there's nothing that leads him to think the blaze is suspicious.
