An 18-year-old has died after jumping from a runaway horse carriage in New York, in a tragedy his family says unfolded when he tried to save his mother.

The horse bolted after breaking free from its driver, sending the carriage out of control. According to the young man's father, his son, Romanch Mahajan, leapt from the carriage in a desperate attempt to help his mother after she fell out of the moving vehicle.

Romanch did not survive the fall. The circumstances surrounding the incident point to a rapidly escalating situation that gave those on board little time to react safely.

Authorities are investigating the incident. The family is grieving the loss of a teenager described as having acted to protect a loved one in a moment of crisis.