Lives and homes are being threatened by an out of control and unpredictable bushfire in Western Australia’s Pilbara region.

A watch and act alert has been issued for people in Tom Price and the western part of Karijini National Park in the Shire of Ashburton.

“There is a possible threat to lives and homes as a fire is approaching the area and conditions are changing,” the Department of Fire and Emergency Services said in a statement issued on Wednesday afternoon.

“You need to leave or get ready to actively defend.”

The bushfire is moving slowly west.

Twenty volunteer Fire and Rescue Service, Bush Fire Service and Department of Parks and Wildlife firefighters are at the scene.

The cause of the fire is unknown.