St. George Fire Department firefighters are investigating the cause of a suspicious Friday morning blaze that damaged a vacant apartment duplex on Ned Avenue.

Firefighters arrived at 8245 Ned Ave. at 1:44 a.m. and found heavy smoke and visible fire near the back door of the rear downstairs unit of the duplex, according to a news release.

Nobody was inside the building at the time of the fire, the release says.

The two ground floor apartments were damaged by the fire while the two upstairs units had smoke damage, the release says.