A road train has jackknifed and caused a pool to smash into a car’s windscreen on a highway south of Perth.

The crash caused a six-car pile-up and significant delays on the Forrest Highway and Old Bunbury Road at Waroona at 11.30am (2.30pm AEDT).

A woman told police how she dodged the swimming pool flying towards her.

A road train has jackknifed and caused a pool to smash into a car's windscreen on a highway south of Perth.
A road train jackknifed on the Forrest Highway. (Nine)
A road train has jackknifed and caused a pool to smash into a car's windscreen on a highway south of Perth.
It caused a pool to crash through a car’s windscreen. (Nine)

”She could see what was going to happen so she ducked for cover and when she looked up there was a steel rod through the screen exactly where her face would have been, so very close for her,” Sergeant Keith Tarver said.

Ten motorists were involved, including two women who were taken to hospital and another two assessed by paramedics.

“[They had] some minor cuts, bruises and scrapes but there’s a bit of shock there,” Tarver said.

A road train has jackknifed and caused a pool to smash into a car's windscreen on a highway south of Perth.
The crash created private school holiday traffic. (Nine)

It’s believed the semi-trailer driver failed to slow for a wide load and investigators are reviewing dashcam footage.

“It appears not every one of the drivers involved here was paying attention and collided with one another,” Tarver said.

The crash caused heavy private school holiday traffic to back up for kilometres.

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