The incident reportedly took place at about 3:30 pm at a home along Cayenne Road, St Augustine.
Two relatives were said to have engaged in an argument during which a 40-year-old reportedly secured a sharp instrument and stabbed Nigel john about the body.
John was taken to the Eric Williams Medical Sciences Complex, Mount Hope, where he died while undergoing treatment.
The 40-year-old relative has since been detained and is said to be cooperating with police.
Earlier in the day, a 35-year-old man was stabbed to death in Morvant by an 18-year-old relative.
More on these reports as they become available.
In a separate incident, police are investigating a report in which a 37-year-old man was shot and killed in Port of Spain on Tuesday morning.