The boy, identified by family friends as Ezra Cornman was digging the tunnel with his brother on the beach when the incident happened in Long Branch around 3:20 p.m. Tuesday.
A police spokesman said the tunnel ran for about six feet and was about two to three feet deep.
The boy's mother called 911 while lifeguards dug him out and performed CPR.
Details on the boy's injuries were not disclosed, but authorities say he regained consciousness after being taken to Monmouth Medical Center. He died Wednesday afternoon.
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