Fire consumed three barns at a hog farm, killing about 1,000 pigs.

The blaze was reported late Monday and not extinguished until about seven hours later, Burlington County Fire Marshal Bob Rose said Tuesday. The cause had not been determined, he said.

The barns had wooden frames but metal roofs and siding.

“With the metal, it acts like an oven,” Rose said.

Two of the barns contained hogs, said Lynne Richmond, a spokeswoman for the state Agriculture Department. All 900 animals in one barn were killed and about 100 more had to be euthanized in a second barn because of smoke inhalation, she said.

The farm had a total of about 1,700 pigs, state police said.