Detectives are working to piece together what caused the death of a man in Brisbane's north-west that left neighbours in shock.

Emergency services were called to a 42-year-old man’s Mitchelton home about midday on Saturday after he had reportedly collapsed and CPR was performed.

A police officer stands at the units in Osborne Road, Mitchelton. Credit:Jocelyn Garcia

A neighbour at the Osborne Road unit complex said he heard shouting coming from the man's unit late on Saturday morning but thought nothing of it at the time.

"There's always noises around here but it wasn't until I saw the ambulance and police cars everywhere that I realised something happened," he said.