Brisbane City Council has announced it will not be installing barricades on the Story Bridge after an apparent murder-suicide yesterday.

Council said it will install phones and 'help' signs on the bridge instead of railing despite research showing it reduces suicide rates.

Forty-year-old Jason Lees and his two-year-old son were both killed after Mr Lees allegedly threw the child from the bridge before jumping to his own death.

Police say a witness saw Mr Lees ride his bike over the footpath on the outbound side of the bridge before committing the acts.

A shift worker has told Brisbane Times he witnessed the tragedy and heard the 'blood-curdling scream' of the child.

"I just heard this scream, it was blood curdling," Craig Cooper told Fairfax Media.

"I don't think I could describe it, it was unbelievable. I caught a glimpse of a falling thing, it was tiny.

"A few seconds later, he (Mr Lees) jumped, it was unmistakeable this time that it was a body."

Mr Lees has been described as a "highly regarded" schoolteacher.

Anglican Church Grammar School's headmaster Jonathan Hensman has released a statement naming the dead man as Jason Lees.

"Churchie is deeply saddened by the sudden passing of one of its prep school teachers," the statement says.

"Jason Lees was a highly regarded and much loved teacher whose kindness to his students, his gentlemanly approach and enthusiasm for teaching were appreciated by students, parents and his colleagues."

He said Mr Lee was a team player and that staff who worked closely with him admired his passion and commitment.

"The impact this sudden news has had on our community is significant and as we work through our grief we are concerned for our boys whom he taught in the classroom or coached on the sports field," the statement said.

He said the school will provide counselling for students and staff.

Mr Lee and his son fell from the bridge about 3.20am (AEST).

Their bodies were found later that morning on the south side of the bridge.

Detective-Superintendent Michael Niland would not comment on the circumstances of the man's death and whether it was being treated as murder suicide.

He also declined to say if Mr Lees was in a custody battle.

"It is a terrible family tragedy and the family are very upset," Det-Supt Michael Niland told reporters in Brisbane.

"The family are suffering an immense amount of grief at the moment.

"They are very sensitive to the issue and have asked not to have anything (reported) in the media."

He said several people witnessed the tragedy.

"There are witnesses to this event," he said.

"We have been gathering statements ... and investigations are continuing."

Premier Anna Bligh said preliminary investigations showed the boy was not known to the Department of Community Safety.

"It is nothing short of a heartbreaking tragedy, and there is a family out there in a lot of pain today," Ms Bligh told reporters in Rockhampton.

Last year, a Brisbane mother left her son in a car on the same bridge before committing suicide, after she had killed her 14-year-old daughter in their Paddington home.

If you are concerned about the mental health of yourself or a loved one, seek support and information by calling Lifeline 13 11 14, Mensline 1300 789 978, or Kids Helpline 1800 551 800

Brisbane's Story Bridge