Police set up a crime scene at a home in Canley Heights in southwest Sydney after the men self-presented to two nearby hospitals.
A 28-year-old and a 32-year-old arrived at Liverpool Hospital about 8.30pm on Tuesday with multiple wounds.
While the younger man was treated for a gunshot injury, he died a short time later.
The 32-year-old is in hospital with a neck injury and remains in a serious but stable condition.
About 10 minutes later, two other men - a 23-year-old and a 22-year-old - presented to Fairfield Hospital in serious conditions before being moved to other hospitals for further treatment.
The 23-year-old received care for a gunshot wound to the neck and the other was treated for a shoulder injury.
The fifth man, a 19-year-old, arrived at Liverpool Hospital an hour later with injuries to his arm, and remains in a stable condition.
"Initial information indicates the men were all injured during a shooting at the home earlier in the night," NSW Police said in a statement.
Officers were seen swarming around the hospitals' emergency wards in the late hours of the night as an investigation was launched into the incident.
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