Police says two young girls have been killed in a high-speed crash in Brisbane's south-west early this morning.

A car ran off the road and slammed into a power pole at Anstead about 3:30am (AEST).

Those at the scene say the vehicle is unrecognisable and the girls inside would have been killed instantly.

Earlier, Inspector Paul James said the power pole was in danger of falling over and had to be stabilised before the scene could be closely examined.

"It would appear that speed has been a factor in the crash," he said.

Police say the bodies of two young girls from the local area have been found at the wreckage.

Forensic crash officers are expected to take several hours to investigate.