MILLVILLE — Authorities are investigating the cause of a second fire at vacant duplexes in less than two weeks.

Firefighters fought a blaze at 312 E. Vine St. at 4:10 a.m. Monday, Fire Department Capt. John Wettstein said.

The fire caused significant damage to that property and the other half of the duplex at 310 E. Vine St., he said.

The fire was brought under control at 6:30 a.m., Wettstein said. Local firefighters were back at the station by 9 a.m.

Wettstein said the fire appeared to have started in the rear of the house, possibly on a porch. Investigators are working to determine the exact cause, he said.

The other fire occurred about 5 a.m. Aug. 28 at a vacant duplex on Oak Street near High Street. Flames broke out at the site later in the day, prompting firefighters to return to the scene.

Wettstein said the cause of the Oak Street fire appeared to be “incendiary” in nature, meaning it was likely set accidentally or on purpose. The exact cause of the fire remained under investigation, he said.

No injuries were reported during the either of the fires, officials said.

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