A crash that killed a Queensland mother and her four children may have been deliberate.

Police are looking at whether the crash near Kingaroy on Monday was a murder-suicide.

RELATED: Kingaroy car crash: Tributes flow for Charmaine McLeod and her four children

A note, believed to written by mother Charmaine Harris McLeod, was found near the scene by investigators, The Courier-Mail reported.

McLeod, 35, and her children Aaleyn, 6, Matilda, 5, Wyatt, 4, and Zaidok, 2, died in the collision with a truck.

Queensland Police Commissioner Ian Stewart said on Friday they have not been added to the official road toll because there is a possibility the crash was not an accident.

Emergency crews devastated

The tragic crash has left emergency crews, who fought through flames to reach the family, devastated they could not save them.

"This is a catastrophic incident scene, it's certainly one of the worst accidents I've ever seen," a police spokesman said.

Aaleyn, 6, Matilda, 5, Wyatt, 4, and Zaidok, 2, died in the collision with a truck. Credit: 7NEWS

Charmaine Harris McLeod and her four young children died in a head-on crash in Queensland on Monday. Credit: AAP

The truck driver was also injured but managed to free himself as the blaze spread to the surrounding grass.

Police say McLeod was trying to overtake when her car slammed into the truck, which was travelling in the opposite direction.

They've also called for any dashcam footage to help them piece together exactly what happened.

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or Beyond Blue on 1300 22 4636.