Australia's Prime Minister has described the murders of eight children at a house in Cairns as "heartbreaking" and an "unspeakable crime".

It's understood seven of the children - aged from 18 months to 15 years - are siblings and one is a relative.

The mother of the seven children is being treated for injuries - thought to be a stab wound to the chest.

A 20 year old brother of the seven siblings is believed to have discovered the bodies.

Amy Stewart - Journalist with 4CA News in Cairns - says no arrests have been made, but police are understood to be speaking to two people: