Two in critical condition after head-on smash in Brisbane's south

Two people are in critical condition after a two-car smash on Brisbane's southside on Thursday.

The cars collided head-on near the intersection of Toohey Road and Barnehurst Street in Tarragindi about 8.30pm.

Two occupants of a Mazda 3, a man and a woman, were rushed to hospital and on Friday morning remained in a critical condition in the Princess Alexandra Hospital.

The three people in the other car, a Mazda 6, were also injured but not as seriously.

The road was closed overnight as Forensic Crash Unit investigators examined the scene.

Police are investigating whether speed was a factor.