North West Ambulance Service were called to reports a ten-day-old boy had been found unresponsive in Lockside Road, Ashton-on-Ribble, on Tuesday (September 21).
The baby boy was rushed to hospital for treatment but died a short time later, police said.
Officers were called to the scene by paramedics at around 2.05am.
A spokesman for Lancashire Police said: "The death is currently being treated as unexplained and our enquiries are ongoing."
Two police cars and a forensic van were spotted in the area by residents this afternoon.
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