Police are investigating a suspicious fire at a home south of Brisbane where the words "FU YOR DEAD" have been spraypainted across the house.

Louie Naumovski from the Logan House Fire Support Network said it looked like the Woodridge house where a woman and six children lived had been firebombed.

Police are investigating a suspicious fire in Woodridge. Credit:Nine Network

"Someone's just chucked something through the window and it's caught alight," he said.

A police spokesman said officers would investigate the scene on Monday, including whether the fire was deliberately lit.