Police are investigating a triple stabbing at Redbank Plains south-west of Brisbane. 

Authorities say four people were involved in an alleged assault at the intersection of Mount Juillerat Drive and School Road about 5pm. 

A man in his 30s is in a serious but stable condition at the Princess Alexandra Hospital, with stab wounds to his back and legs.

Two others were also hospitalised: a second man in his 30s with a head injury and a man in his 20s with a shoulder injury. 

A Queensland Police Service spokesperson said two people have been detained and were assisting with enquiries.

Anyone with information is urged to contact police.