A man has died after starting a fire inside a unit on the NSW South Coast.

Emergency services were called to Ritchie St in Bomaderry about 1.15pm on Thursday following reports of a concern for welfare. 

Police arrived to find a man barricaded inside a unit, where he had started a fire.

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A perimeter was established as a police operation got underway, with residents urged to avoid the area.

Officers entered the unit about 3.30pm and found a 57-year-old man inside.

The fire was still burning and was later extinguished by Fire and Rescue NSW.

The man was treated at the scene but could not be saved.

He is yet to be formally identified. 

A crime scene was established and a critical incident was declared. 

The critical incident investigation will examine the circumstances surrounding the man’s death.

A report will be prepared for the coroner.