Police and paramedics were called to a block of flats opposite the Pleasant Retreat pub in Watkin Lane at 12.20pm.
A 35-year-old man was found unresponsive and pronounced dead at the scene.
The circumstances of his death have not been confirmed.
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A number of police cars and a CSI van were seen outside the building yesterday afternoon.
The building was later cordoned off as forensics investigated the scene.
A spokesman for Lancashire Police said: "We were called at 12.20pm yesterday (April 4) to reports of a sudden death at an address on Watkin Lane in Lostock Hall.
"Officers and paramedics attended and sadly a 35-year-old man was pronounced dead at the scene.
"His death is not being treated as suspicious."